Test Patterns and Conventions¶

Analysis Date: January 13, 2026
Updated: January 28, 2026 (Added ExecutorUtils tests, renamed serializer folders) Total Unit Test Files Analyzed: 247
Framework: JUnit 5 (Jupiter) + AssertJ + Mockito

CRITICAL RULE: ONE METHOD, ONE TEST FILE¶

ABSOLUTE REQUIREMENT: Each test file MUST test exactly ONE method (with permuted input and context setups fo vaious scenarios).

CORRECT Examples:¶

getSslContextTests.java - Tests ONLY the getSslContext() method
buildDefaultTests.java - Tests ONLY the buildDefault() static method
buildTests.java - Tests ONLY the build() method of a builder class
closeTests.java - Tests ONLY the close() method
serializeTests.java - Tests ONLY the serialize() method

INCORRECT Examples (NEVER DO THIS):¶

sslContextTests.java - Too generic, doesn't specify method name
builderTests.java - Too generic, builder is a method not a concept
edgeCasesTests.java - Too generic, edge cases belong in method-specific files
utilityMethodsTests.java - Testing multiple methods in one file
helperTests.java - Too vague, no specific method

Rule Application:¶

Find the method name in the source code
Create test file: {methodName}Tests.java (camelCase)
All tests in that file test ONLY that method
Different scenarios for the same method go in the SAME file

DO NOT TEST: Constants, Abstract Classes, or Lombok-Generated Code¶

RULE: The following elements should NOT have dedicated test files:

Element	Reason
Static constants/fields (e.g., `MIN_POOL_SIZE`, `MAX_POOL_SIZE`)	Values are self-evident; no behavior to test
Abstract classes directly	Test concrete implementations instead; each impl may have different behavior
Lombok-generated constructors (`@NoArgsConstructor`, `@AllArgsConstructor`, `@RequiredArgsConstructor`)	Auto-generated code with no custom logic
Lombok-generated getters/setters (`@Data`, `@Getter`, `@Setter`)	Auto-generated code with no custom logic

EXCEPTION: Test methods that are manually written and contain validation or business logic:

// This constructor SHOULD be tested - it has validation logic
public Provider(EventListenerTransaction transaction) {
    this.transaction = ValidationUtils.requireNonNull(transaction, "transaction is required");
}

// This setter SHOULD be tested - it has validation logic
public void setConfiguration(MapConfiguration configuration) {
    this.configuration = ValidationUtils.requireNonNull(configuration, "configuration is required");
    this.pattern = ValidationUtils.requireNonBlank(configuration.getString(PATTERN, ""), "pattern is required").trim();
}

// This getter SHOULD be tested - it has custom logic
@Override
public String getId() { return Constants.ID; }

CRITICAL RULE: INHERITED METHODS IN IMPLEMENTATION TESTS¶

ABSOLUTE REQUIREMENT: Inherited methods MUST be tested as part of each implementation's test folder, NOT in a separate parent-level test file.

CORRECT Examples:¶

matchers/globmatcher/acceptTests.java          ← Tests accept() inherited from Matcher
matchers/globmatcher/setConfigurationTests.java ← Tests setConfiguration() (manually written with validation)
matchers/listmatcher/acceptTests.java          ← Same inherited method, tested per implementation

INCORRECT Examples (NEVER DO THIS):¶

matchers/acceptTests.java                      ← WRONG: Testing inherited method at parent level
serializers/getContentTypeTests.java           ← WRONG: Testing all serializers in one file
destinations/setConfigurationTests.java        ← WRONG: Parent-level test for inherited method

Rule Application:¶

Identify inherited methods in base class (e.g., Matcher.accept(), Serializer.getContentType())
Create test file in each implementation folder (e.g., globmatcher/acceptTests.java)
Test the inherited behavior using the concrkete implementation
Each implementation gets its own test file for the inherited method
No parent-level test files for methods that are inherited by implementations

Rationale:¶

Coverage is reported per-class, so inherited methods must be exercised through each subclass
Each implementation may have different setup/configuration requirements
Ensures inherited behavior works correctly with each implementation's specific state

1. Directory Structure¶

1.1 Root Test Directory¶

src/tests/unit-tests/java/io/github/fortunen/kete/

1.2 Package Organization Pattern¶

RULE: Test packages mirror the main source class location, with an additional folder named after the class being tested (in lowercase).

Main Source:                                    Test Location:
src/main/.../ProviderFactory.java       →       src/tests/unit-tests/.../providerfactory/
src/main/.../Provider.java              →       src/tests/unit-tests/.../provider/
src/main/.../Configuration.java         →       src/tests/unit-tests/.../configuration/configuration/
src/main/.../Route.java                 →       src/tests/unit-tests/.../routes/route/
src/main/.../utils/ValidationUtils.java →       src/tests/unit-tests/.../utils/validationutils/
src/main/.../utils/RouteUtils.java      →       src/tests/unit-tests/.../routes/routeutils/
src/main/.../destinations/HttpDestination.java → src/tests/unit-tests/.../destinations/httpdestination/
src/main/.../serializers/JsonSerializer.java   → src/tests/unit-tests/.../serializers/jsonserializer/
src/main/.../matchers/GlobMatcher.java          → src/tests/unit-tests/.../matchers/globmatcher/

1.3 Folder Naming Rules¶

Element	Naming Pattern
Top-level category folders	lowercase plural (e.g., `destinations/`, `serializers/`, `matchers/`, `utils/`, `routes/`)
Class-under-test folder	lowercase class name (e.g., `httpdestination/`, `jsonserializer/`, `globmatcher/`)
Utility class folder	lowercase class name (e.g., `validationutils/`, `templateutils/`, `retryutils/`)

1.4 Complete Folder Structure¶

src/tests/unit-tests/java/io/github/fortunen/kete/
├── configuration/
│   ├── configuration/
│   │   └── constructorTests.java
│   └── configurationutils/
│       ├── constructorTests.java
│       └── getConfigurationTests.java
├── destinations/
│   ├── amqp091destination/
│   ├── amqp1destination/
│   ├── httpdestination/
│   ├── kafkadestination/
│   ├── mqtt3destination/
│   └── mqtt5destination/
├── matchers/
│   ├── globmatcher/
│   ├── listmatcher/
│   ├── regexmatcher/
│   └── sqlmatcher/
├── provider/
├── providerfactory/
├── retries/
│   └── retryutils/
├── routes/
│   ├── route/
│   └── routeutils/
├── serializers/
│   ├── cborserializer/
│   ├── csvserializer/
│   ├── jsonserializer/
│   ├── propertiesserializer/
│   ├── smileserializer/
│   ├── tomlserializer/
│   ├── xmlserializer/
│   └── yamlserializer/
└── utils/
    ├── certificateutils/
    ├── configurationutils/
    ├── destinationutils/
    ├── executorutils/
    ├── fileutils/
    ├── iocutils/
    ├── matcherutils/
    ├── metricsutils/
    ├── retryutils/
    ├── routeutils/
    ├── serializerutils/
    ├── templateutils/
    └── validationutils/

2. File Naming¶

2.1 Pattern¶

RULE: {methodName}Tests.java (camelCase, suffix Tests)

2.2 Examples¶

Method Being Tested	File Name
`close()`	`closeTests.java`
`constructor`	`constructorTests.java`
`serialize()`	`serializeTests.java`
`accept()`	`acceptTests.java`
`setConfiguration()`	`setConfigurationTests.java`
`getConfiguration()`	`getConfigurationTests.java`
`createEventExecutor()`	`createEventExecutorTests.java`
`shutdownExecutor()`	`shutdownExecutorTests.java`
`getSslContext()`	`getSslContextTests.java`
`requireNonNull()`	`requireNonNullTests.java`
`tryParseInt()`	`tryParseIntTests.java`
`isEmpty()` for Array	`isEmpty_ArrayTests.java`
`isEmpty()` for Collection	`isEmpty_CollectionTests.java`
`requireGreaterThan()` for int	`requireGreaterThan_intTests.java`
`requireGreaterThan()` for long	`requireGreaterThan_longTests.java`

2.3 Overloaded Method Naming¶

RULE: For overloaded methods, append _{paramketerType} or _{distinguisher} to the file name.

isEmpty(Object[])      → isEmpty_ArrayTests.java
isEmpty(byte[])        → isEmpty_ByteArrayTests.java
isEmpty(Collection<?>)  → isEmpty_CollectionTests.java
isEmpty(Map<?,?>)      → isEmpty_MapTests.java
isEmpty(String)        → isEmpty_StringTests.java
requireInRange(int)    → requireInRange_intTests.java
requireInRange(long)   → requireInRange_longTests.java

3. Package Declaration¶

3.1 Pattern¶

RULE: Package name matches the folder structure exactly, with class-under-test folder name matching folder case.

3.2 Standard Examples¶

// For providerfactory/closeTests.java
package io.github.fortunen.kete.providerfactory;

// For routes/route/acceptTests.java
package io.github.fortunen.kete.routes.route;

// For utils/validationutils/requireNonNullTests.java
package io.github.fortunen.kete.utils.validationutils;

// For serializers/jsonserializer/serializeTests.java
package io.github.fortunen.kete.serializers.jsonserializer;

// For destinations/httpdestination/setConfigurationTests.java
package io.github.fortunen.kete.destinations.httpdestination;

3.3 Utility Class Package Convention¶

RULE: All utility test packages use lowercase subfolder names matching the convention:

// For retries/retryutils/getRetryTests.java
package io.github.fortunen.kete.unittests.retries.retryutils;

// For routes/routeutils/getRouteTests.java  
package io.github.fortunen.kete.unittests.routes.routeutils;

// For matchers/matcherutils/getMatchersTests.java
package io.github.fortunen.kete.unittests.matchers.matcherutils;

// For utils/tlsutils/getSslContextTests.java
package io.github.fortunen.kete.unittests.utils.tlsutils;

NOTE: Always use lowercase for package names to maintain consistency across the codebase.

4. Imports¶

4.1 Static Imports (Always First)¶

RULE: Use static imports with wildcards for test utilities. Order: AssertJ → Mockito.

import static org.assertj.core.api.Assertions.*;
import static org.mockito.ArgumentMatchers.*;
import static org.mockito.Mockito.*;

4.2 Common Static Import Combinations¶

// Minimum for simple tests
import static org.assertj.core.api.Assertions.assertThat;

// For exception testing
import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.catchThrowable;

// For exception-free testing
import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatCode;

// For exception type + message testing
import static org.assertj.core.api.Assertions.assertThatThrownBy;

// For mocking
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.never;
import static org.mockito.Mockito.doThrow;
import static org.mockito.Mockito.mockStatic;

// For matchers
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.ArgumentMatchers.eq;
import static org.mockito.ArgumentMatchers.anyString;
import static org.mockito.ArgumentMatchers.argThat;

4.3 Regular Imports¶

RULE: Standard imports follow static imports. Group by: project classes → external libraries → JDK.

// Project imports
import io.github.fortunen.kete.ProviderFactory;
import io.github.fortunen.kete.utils.ValidationUtils;

// External library imports
import org.apache.commons.configuration2.MapConfiguration;
import org.junit.jupiter.api.Test;
import org.keycloak.events.Event;

// JDK imports
import java.util.HashMap;
import java.util.Map;

5. Class Declaration¶

5.1 Class Visibility¶

RULE: Class visibility is MIXED. Both patterns exist:

// Package-private (no modifier) - COMMON
class closeTests {

// Public - COMMON  
public class serializeTests {

public class requireNonNullTests {

public class acceptTests {

OBSERVATION: No clear pattern. Both are acceptable.

5.2 Class Name¶

RULE: Class name matches the file name exactly (camelCase starting lowercase + Tests).

class closeTests { }
class constructorTests { }
public class serializeTests { }
public class requireNonNullTests { }
public class acceptTests { }

5.3 No Class Annotations¶

RULE: Test classes have NO annotations. No @ToString, no @DisplayName, no @TestInstance.

6. Test Method Declaration¶

6.1 Visibility¶

RULE: Method visibility is MIXED. Both patterns exist:

// Package-private (no modifier) - COMMON
@Test
void shouldShutdownEventExecutorOnClose() {

// Public - COMMON
@Test
public void shouldSerializeEventToJson() {

OBSERVATION: Package-private tends to appear in providerfactory/, provider/, configuration/. Public tends to appear in utils/, serializers/, filters/, destinations/.

6.2 Method Naming Pattern¶

RULE: should{ExpectedBehavior}[When{Condition}]

6.3 Examples by Category¶

Success Cases:

shouldCreateInstanceWithNoArgConstructor()
shouldInitializeContainersAfterConstruction()
shouldReturnValueWhenNotNull()
shouldParsePositiveInteger()
shouldMatchExactString()
shouldSetBasicConfiguration()
shouldSerializeEventToJson()
shouldAcceptWhenFiltersEmpty()
shouldSendEvent()
shouldShutdownEventExecutorOnClose()

Failure/Edge Cases:

shouldThrowWhenConfigurationIsNull()
shouldThrowWhenUrlMissing()
shouldThrowWhenNameIsNull()
shouldThrowWhenNameIsEmpty()
shouldThrowWhenNameIsBlank()
shouldReturnEmptyForNull()
shouldReturnEmptyForEmptyString()
shouldReturnEmptyForBlankString()
shouldReturnEmptyForInvalidString()
shouldNotMatchDifferentString()
shouldRejectWhenAnyFilterRejects()
shouldNotSendWhenEventTypeNull()
shouldNotSendWhenEventTypeEmpty()
shouldNotSendWhenEventBodyEmpty()

Conditional Cases:

shouldInvertMatchWithNot()
shouldAllowMultipleCloseCalls()
shouldHandleEmptyPattern()
shouldHandleEmptyEventType()
shouldHandleEventHavingNullType()
shouldResizeThreadPoolWhenConfiguredDifferently()
shouldDisposeRouteOnInitializationFailure()

7. Test Method Structure (AAA Pattern)¶

7.1 Required Sections¶

RULE: Every test method MUST use AAA comments. This structure is MANDATORY and RELIGIOUSLY adhered to without exceptions.

7.2 Standard Structure¶

@Test
void shouldDoSomething() {

    // arrange

    var instance = new ClassUnderTest();
    var input = "test-input";

    // act

    var result = instance.methodUnderTest(input);

    // assert

    assertThat(result).isNotNull();
}

7.3 Whitespace Rules (STRICT - NO EXCEPTIONS)¶

Location	Rule	Mandatory
After method opening brace `{`	ONE blank line
BEFORE `// arrange` comment	ONE blank line (the one after `{`)
AFTER `// arrange` comment	ONE blank line
BEFORE `// act` comment	ONE blank line
AFTER `// act` comment	ONE blank line
BEFORE `// assert` comment	ONE blank line
AFTER `// assert` comment	ONE blank line
Before method closing brace `}`	ZERO blank lines

7.4 Visual Template (Copy This Exactly)¶

@Test
public void shouldDescribeExpectedBehavior() {
                                           // ← blank line after {
    // arrange
                                           // ← blank line after // arrange
    var instance = new ClassUnderTest();
    var input = "test-input";
                                           // ← blank line before // act
    // act
                                           // ← blank line after // act
    var result = instance.methodUnderTest(input);
                                           // ← blank line before // assert
    // assert
                                           // ← blank line after // assert
    assertThat(result).isNotNull();
}                                          // ← NO blank line before }

7.4 Section Variations¶

Arrange Only (for constructor tests without method call):

@Test
void shouldCreateInstanceWithNoArgConstructor() {

    // act

    var instance = new ClassUnderTest();

    // assert

    assertThat(instance).isNotNull();
}

Act + Assert Combined:

@Test
void shouldDisposeContainerOnClose() {

    // arrange

    var factory = new ProviderFactory();

    // act & assert

    assertThatCode(() -> factory.close()).doesNotThrowAnyException();
}

Act & Assert for Exceptions:

@Test
public void shouldThrowWhenUrlMissing() {

    // arrange

    var destination = new HttpDestination(templateUtils, configUtils);
    var config = new MapConfiguration(new HashMap<>());

    // act

    var thrown = catchThrowable(() -> {
        destination.setConfiguration(config);
    });

    // assert

    assertThat(thrown).isInstanceOf(Exception.class);
}

7.5 Cleanup Section (Rare)¶

@Test
void shouldCreateExecutorWithSpecifiedPoolSize() {

    // act

    ExecutorService executor = ExecutorUtils.createEventExecutor(5);

    // assert

    assertThat(executor).isNotNull();

    // cleanup

    executor.shutdownNow();
}

8. Variable Declarations¶

8.1 Primary Pattern: `var`¶

RULE: Use var for ALL local variable declarations when type is inferrable.

var factory = new ProviderFactory();
var destination = mock(Destination.class);
var config = new MapConfiguration(new HashMap<>());
var result = instance.methodUnderTest();
var thrown = catchThrowable(() -> { ... });

8.2 Explicit Type Exceptions¶

RULE: Use explicit type when: 1. Type cannot be inferred (null assignment) 2. Explicit type provides clarity for complex generics 3. Array initialization

String value = null;
MapConfiguration config = null;
ExecutorService executor = ExecutorUtils.createEventExecutor(5);
Event event = null;

8.3 Static Fields¶

RULE: Static fields use explicit types with private static final.

private static final ObjectMapper MAPPER = new ObjectMapper();
private static final byte[] EMPTY_BYTES = new byte[0];

9. Assertions (AssertJ)¶

9.1 Basic Assertions¶

// Not null
assertThat(result).isNotNull();

// Null
assertThat(result).isNull();

// Equality
assertThat(result).isEqualTo(expected);
assertThat(result).isNotEqualTo(unexpected);

// Same instance
assertThat(result).isSameAs(original);

// Boolean
assertThat(result).isTrue();
assertThat(result).isFalse();

// Empty collections/strings
assertThat(result).isEmpty();
assertThat(result).isNotEmpty();

// Size
assertThat(result).hasSize(5);
assertThat(result.length).isEqualTo(3);

9.2 String Assertions¶

assertThat(result).isEqualTo("expected");
assertThat(result).startsWith("prefix");
assertThat(result).contains("substring");
assertThat(result.contains("text")).isTrue();

9.3 Collection Assertions¶

assertThat(list).hasSize(3);
assertThat(array.length).isEqualTo(0);
assertThat(result).isNotNull();
assertThat(result.length).isEqualTo(0);

9.4 Optional Assertions¶

assertThat(ValidationUtils.tryParseInt("123")).hasValue(123);
assertThat(ValidationUtils.tryParseInt("abc")).isEmpty();

9.5 Exception Assertions¶

Pattern 1: catchThrowable + assert (MOST COMMON)

var thrown = catchThrowable(() -> {
    instance.methodThatThrows(badInput);
});

assertThat(thrown).isInstanceOf(IllegalStateException.class);
assertThat(thrown.getMessage()).isEqualTo("expected message");
assertThat(thrown.getMessage()).contains("partial text");

Pattern 2: assertThatThrownBy (for concise exception + message)

assertThatThrownBy(() -> factory.onEvent(null))
    .isInstanceOf(IllegalStateException.class)
    .hasMessageContaining("providerEvent is required");

Pattern 3: assertThatCode for no-exception verification

assertThatCode(() -> factory.close()).doesNotThrowAnyException();

9.6 Compound Boolean in Assertions¶

assertThat(result.length > 0).isTrue();
assertThat(json.contains("\\n") || json.contains("\\t")).isTrue();

10. Mocking (Mockito)¶

10.1 Creating Mocks¶

RULE: Always use mock() method, never @Mock annotations.

var session = mock(KeycloakSession.class);
var destination = mock(Destination.class);
var filter = mock(Filter.class);

10.2 Stubbing¶

// Return value
when(session.realms()).thenReturn(realmProvider);
when(filter.accept(anyString())).thenReturn(true);

// Chain stubbing
when(configUtils.getConfiguration(any())).thenReturn(configuration);
when(configuration.isMetricsEnabled()).thenReturn(true);

// Throw exception
doThrow(new RuntimeException("init failed")).when(route).initialize();

10.3 Verification¶

// Verify called once
verify(destination).sendMessage(any(EventMessage.class));

// Verify called specific times
verify(destination, times(1)).sendMessage(any());
verify(mockTransaction, times(3)).addEvent(any(Event.class));

// Verify never called
verify(destination, never()).sendMessage(any(EventMessage.class));

// Verify with argument matcher
verify(destination, times(1)).sendMessage(argThat(m ->
    "eventId".equals(m.eventId()) &&
    "LOGIN".equals(m.eventType())));

verify(mockTransaction, times(1)).addEvent(ArgumentMatchers.argThat(arg ->
    arg != null && "test-id".equals(arg.getId())
));

10.4 Static Mocking¶

try (var mockedUtils = mockStatic(KeycloakModelUtils.class)) {

    mockedUtils.when(() -> KeycloakModelUtils.runJobInTransaction(any(), any()))
        .thenAnswer(invocation -> null);

    // test code here

    mockedUtils.verify(() -> KeycloakModelUtils.runJobInTransaction(sessionFactory, factory));
}

11. Test Data Creation¶

11.1 Inline Object Creation¶

RULE: Create test data inline in the arrange section. No shared fixtures.

// Simple objects
var event = new Event();
event.setType(EventType.LOGIN);
event.setRealmId("test-realm");

// Maps for configuration
var config = new MapConfiguration(Map.of(
    "url", "http://localhost:8080/events",
    "method", "POST"
));

// Or with HashMap for mutable maps
var map = new HashMap<String, Object>();
map.put(RetryUtils.ENABLED, true);
var config = new MapConfiguration(map);

11.2 Helper Methods¶

RULE: Private helper methods within test class for complex or repeated setup.

private EventMessage createMessage(String eventId, String realm, boolean isAdminEvent, 
        String eventType, String contentType, byte[] eventBody, 
        String resourceType, String operationType) {
    return EventMessage.get()
        .eventId(eventId != null ? eventId : "")
        .realm(realm != null ? realm : "")
        .isAdminEvent(isAdminEvent)
        .eventType(eventType != null ? eventType : "")
        .contentType(contentType != null ? contentType : "")
        .eventBody(eventBody != null ? eventBody : EMPTY_BYTES)
        .resourceType(resourceType != null ? resourceType : "")
        .operationType(operationType != null ? operationType : "");
}

11.3 Private Inner Classes¶

RULE: Use private static inner classes for test-specific types.

private static class ComplexObject {
    String data;
    int number;

    ComplexObject(String data, int number) {
        this.data = data;
        this.number = number;
    }
}

private static class CustomCheckedException extends Exception {
    public CustomCheckedException(String message) {
        super(message);
    }
}

private static class TestJsonProcessingException extends JsonProcessingException {
    protected TestJsonProcessingException(String msg) {
        super(msg);
    }
}

12. Test Organization Within File¶

12.1 Logical Grouping¶

RULE: Group related tests. Use comment dividers for sections in large files.

// =========================================================================
// ID
// =========================================================================

@Test
public void shouldHaveCorrectId() { ... }

// =========================================================================
// Header Constants
// =========================================================================

@Test
public void shouldHaveCorrectEventIdHeader() { ... }

@Test
public void shouldHaveCorrectEventTypeHeader() { ... }

12.2 Test Order¶

PATTERN: Happy path first, then edge cases, then error cases.

Basic success cases
Variations of success cases
Empty/null handling (returns default)
Error cases (throws exception)
Edge cases

13. Comments¶

13.1 Allowed Comments¶

Type	Example	Allowed
AAA section markers	`// arrange`	YES (REQUIRED)
Combined section	`// act & assert`	YES
Section dividers	`// =========`	YES
Cleanup section	`// cleanup`	YES
Brief clarification in assert	`// assert - Jackson serializes null to "null"`	YES

13.2 Prohibited Comments¶

Type	Allowed
Method-level Javadoc	NO
Inline explanatory comments	NO
TODO comments	NO
Implementation detail comments	NO

14. Exception Testing Patterns¶

14.1 Null Paramketer Tests¶

@Test
public void shouldThrowWhenNameNull() {

    // arrange

    var utils = new SomeUtils();

    // act

    var thrown = catchThrowable(() -> {
        utils.method(null, validParam);
    });

    // assert

    assertThat(thrown).isInstanceOf(IllegalStateException.class);
}

14.2 Empty/Blank String Tests¶

@Test
public void shouldThrowWhenNameEmpty() {
    // ... 
    utils.method("", validParam);
    // ...
}

@Test
public void shouldThrowWhenNameBlank() {
    // ...
    utils.method("   ", validParam);
    // ...
}

14.3 Exception Message Verification¶

// Exact message
assertThat(thrown.getMessage()).isEqualTo("name is required");

// Contains
assertThat(thrown.getMessage()).contains("required");
assertThatThrownBy(() -> ...).hasMessageContaining("is required");

15. Complete Test File Template¶

package io.github.fortunen.kete.{category}.{classname};

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.catchThrowable;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

import io.github.fortunen.kete.{ClassUnderTest};
import org.junit.jupiter.api.Test;

public class {methodName}Tests {

    @Test
    public void shouldSucceedWithValidInput() {

        // arrange

        var instance = new ClassUnderTest();
        var input = "valid-input";

        // act

        var result = instance.methodUnderTest(input);

        // assert

        assertThat(result).isNotNull();
        assertThat(result).isEqualTo("expected");
    }

    @Test
    public void shouldThrowWhenInputNull() {

        // arrange

        var instance = new ClassUnderTest();

        // act

        var thrown = catchThrowable(() -> {
            instance.methodUnderTest(null);
        });

        // assert

        assertThat(thrown).isInstanceOf(IllegalStateException.class);
        assertThat(thrown.getMessage()).contains("input is required");
    }

    @Test
    public void shouldReturnDefaultWhenInputEmpty() {

        // arrange

        var instance = new ClassUnderTest();

        // act

        var result = instance.methodUnderTest("");

        // assert

        assertThat(result).isEmpty();
    }
}

16. Anti-Patterns (NEVER USE)¶

Anti-Pattern	Reason
`@Mock` annotations	Use `mock()` method instead
`@InjectMocks`	Manual dependency injection
`@BeforeEach` / `@AfterEach`	Inline setup in each test (for unit tests)
`@DisplayName`	Method name is self-documenting
`@ToString` on test class	Not needed
`@Nested` classes	One file per method
JUnit 5 assertions	Use AssertJ
Shared mutable state	Each test independent
Test fixtures / builders	Inline data creation
`@ParamketerizedTest`	Separate explicit tests
Comments explaining code	Self-documenting tests
Testing constants/static fields	No utility - values are self-evident
Testing abstract classes directly	Test concrete implementations instead
Testing Lombok-generated constructors	Only test manually-written constructors with logic
Testing Lombok-generated getters/setters	Only test manually-written accessors with logic

17. Checklist for New Test Files¶

[ ] Package matches folder structure
[ ] File name: {methodName}Tests.java
[ ] Class name matches file name
[ ] Static imports for AssertJ and Mockito
[ ] Each test uses AAA comments
[ ] Blank line after each section comment
[ ] Use var for local variables
[ ] Method name starts with should
[ ] No @BeforeEach / @AfterEach (inline setup)
[ ] No class-level annotations
[ ] Use catchThrowable for exception testing
[ ] Use assertThat() from AssertJ
[ ] Use mock() not @Mock
[ ] Test data created inline

18. File Count by Category¶

Category	Files
utils/validationutils/	68
serializers/	16
matchers/	8
providerfactory/	9
destinations/	10
routes/	7
provider/	5
configuration/	3
retries/	2
utils/ (other)	12
Total	140

19. Testing Philosophy & Quality Standards¶

19.1 Core Principles¶

Tests serve as living documentation of the system. They must:

Document Behavior: Tests can be read as a book when in doubt about what the code is supposed to do
Protect Against Regression: Guard the current system against future corruption if maintainers are not careful
Ensure Quality: Verify the correctness of the current system
Provide Maximum Confidence: Cover edge cases not just for coverage metrics, but for real-world confidence

19.2 Test Utility Requirements¶

RULE: Every test MUST have actual utility. No contrived scenarios.

Requirement	Description
Real-world scenarios	Test realistic usage patterns, not artificial constructs
Meaningful assertions	Assert outcomes that matter to the system's behavior
Edge case exploration	Cover boundary conditions that could cause failures in production
Failure mode testing	Verify graceful handling of error conditions

19.3 Assertion Completeness¶

RULE: Assert the FULL state of the outcome. Partial assertions are insufficient.

//  BAD - Partial assertion
assertThat(result).isNotNull();

//  GOOD - Complete state verification
assertThat(result).isNotNull();
assertThat(result.getId()).isEqualTo("expected-id");
assertThat(result.getName()).isEqualTo("expected-name");
assertThat(result.isEnabled()).isTrue();
assertThat(result.getItems()).hasSize(3);
assertThat(result.getItems()).containsExactly("item1", "item2", "item3");

19.4 Exception Message Assertion¶

RULE: EXACT exception messages MUST be asserted. This documents the API contract.

//  BAD - Only checking exception type
assertThat(thrown).isInstanceOf(IllegalStateException.class);

//  BAD - Partial message check
assertThat(thrown.getMessage()).contains("required");

//  GOOD - Exact message assertion
assertThat(thrown)
    .isInstanceOf(IllegalStateException.class)
    .hasMessage("url is required");

19.5 AssertJ Expressiveness¶

WHY AssertJ: Chosen for its expressiveness (inspired by Shouldly in C#). Leverage the fluent API for clarity.

// Leverage AssertJ's expressive assertions
assertThat(result)
    .isNotNull()
    .isInstanceOf(Configuration.class)
    .extracting(Configuration::isMetricsEnabled)
    .isEqualTo(false);

assertThat(routes)
    .hasSize(3)
    .extracting(Route::getName)
    .containsExactlyInAnyOrder("route-1", "route-2", "route-3");

assertThat(exception)
    .isInstanceOf(IllegalStateException.class)
    .hasMessage("bootstrap.servers is required")
    .hasNoCause();

20. Serializer Testing Requirements¶

20.1 Round-Trip Verification¶

RULE: Serializer tests MUST parse the result to create a copy that is 100% compared to the input data.

@Test
public void shouldSerializeAndDeserializeEventWithAllFields() {

    // arrange

    var serializer = new JsonSerializer();
    var event = new Event();
    event.setId("test-id");
    event.setType(EventType.LOGIN);
    event.setRealmId("test-realm");
    event.setUserId("test-user");
    event.setClientId("test-client");
    event.setSessionId("test-session");
    event.setIpAddress("192.168.1.1");
    event.setTime(1704067200000L);
    event.setDetails(Map.of("key1", "value1", "key2", "value2"));

    // act

    var serialized = serializer.serialize(event);

    // assert - Parse back and verify Complete equality

    var parsed = MAPPER.readTree(serialized);
    assertThat(parsed.get("id").asText()).isEqualTo("test-id");
    assertThat(parsed.get("type").asText()).isEqualTo("LOGIN");
    assertThat(parsed.get("realmId").asText()).isEqualTo("test-realm");
    assertThat(parsed.get("userId").asText()).isEqualTo("test-user");
    assertThat(parsed.get("clientId").asText()).isEqualTo("test-client");
    assertThat(parsed.get("sessionId").asText()).isEqualTo("test-session");
    assertThat(parsed.get("ipAddress").asText()).isEqualTo("192.168.1.1");
    assertThat(parsed.get("time").asLong()).isEqualTo(1704067200000L);
    assertThat(parsed.get("details").get("key1").asText()).isEqualTo("value1");
    assertThat(parsed.get("details").get("key2").asText()).isEqualTo("value2");
}

20.2 Edge Cases for Serializers¶

Edge Case	Must Test
All fields populated
All fields null
Empty strings
Unicode characters
Special characters (newlines, tabs, quotes)
Very long strings
Nested structures
Null event/adminEvent object

21. Destination Testing Requirements¶

21.1 Unit Test Scope for Destinations¶

UNDERSTANDING: Integration tests achieve maximum effect for destinations, but unit tests MUST cover:

Scenario	Unit Testable	Approach
Configuration validation		Test setConfiguration with invalid/missing values
Constructor behavior		Verify dependencies are set
Connection failure handling		Mock connection factories to throw
Message send when disconnected		Mock clients in error state
Resource cleanup on close		Verify close methods called on mocks
Retry behavior		Mock failures, verify retry invocation

21.2 Unconnected Destination Behavior¶

RULE: Test behavior when destinations cannot connect (no RabbitMQ, Kafka, etc.)

@Test
public void shouldThrowWhenBrokerUnreachable() {

    // arrange

    var destination = new KafkaDestination(templateUtils, configUtils);
    var config = new MapConfiguration(Map.of(
        "bootstrap.servers", "unreachable:9092",
        "topic", "test-topic"
    ));
    destination.setConfiguration(config);

    // act

    var thrown = catchThrowable(() -> destination.initialize());

    // assert

    assertThat(thrown)
        .isInstanceOf(KafkaException.class)
        .hasMessageContaining("Failed to connect");
}

21.3 HTTP Destination - WireMock Testing¶

RULE: Use MockWebServer or WireMock for full HTTP destination testing in unit tests.

import okhttp3.mockwebserver.MockWebServer;
import okhttp3.mockwebserver.MockResponse;
import okhttp3.mockwebserver.RecordedRequest;

public class sendMessageTests {

    private MockWebServer mockServer;

    @BeforeEach
    void setUp() throws Exception {
        mockServer = new MockWebServer();
        mockServer.start();
    }

    @AfterEach
    void tearDown() throws Exception {
        mockServer.shutdown();
    }

    @Test
    public void shouldSendPostRequestWithEventBody() throws Exception {

        // arrange

        mockServer.enqueue(new MockResponse().setResponseCode(200));

        var destination = new HttpDestination(templateUtils, configUtils);
        var config = new MapConfiguration(Map.of(
            "url", mockServer.url("/events").toString(),
            "method", "POST"
        ));
        destination.setConfiguration(config);
        destination.initialize();

        var message = EventMessage.get()
            .eventId("test-id")
            .eventType("LOGIN")
            .contentType("application/json")
            .eventBody("{\"type\":\"LOGIN\"}".getBytes());

        // act

        destination.sendMessage(message);

        // assert

        RecordedRequest request = mockServer.takeRequest();
        assertThat(request.getMethod()).isEqualTo("POST");
        assertThat(request.getPath()).isEqualTo("/events");
        assertThat(request.getBody().readUtf8()).isEqualTo("{\"type\":\"LOGIN\"}");
        assertThat(request.getHeader("Content-Type")).isEqualTo("application/json");
        assertThat(request.getHeader("EventId")).isEqualTo("test-id");
        assertThat(request.getHeader("EventType")).isEqualTo("LOGIN");
    }

    @Test
    public void shouldHandleServerError() throws Exception {

        // arrange

        mockServer.enqueue(new MockResponse().setResponseCode(500).setBody("Internal Error"));

        var destination = new HttpDestination(templateUtils, configUtils);
        // ... setup ...

        // act

        var thrown = catchThrowable(() -> destination.sendMessage(message));

        // assert

        assertThat(thrown)
            .isInstanceOf(HttpResponseException.class)
            .hasMessage("HTTP 500: Internal Error");
    }
}

NOTE: For HTTP destinations, @BeforeEach and @AfterEach ARE allowed for MockWebServer lifecycle management.

22. Edge Case Testing Requirements¶

22.1 Mandatory Edge Cases¶

Every method under test MUST have tests for:

Category	Cases
Null handling	null input, null in collections, null nested objects
Empty values	empty string `""`, empty collections, empty arrays
Blank values	whitespace-only strings `" "`
Boundary values	0, -1, Integer.MAX_VALUE, Integer.MIN_VALUE
Invalid formats	malformed URLs, invalid JSON, unparseable numbers
Concurrent access	thread safety (where applicable)
Resource exhaustion	very large inputs, many items

22.2 Example: Comprehensive Validation Testing¶

// Test NULL
@Test
public void shouldThrowWhenValueNull() { ... }

// Test EMPTY
@Test
public void shouldThrowWhenValueEmpty() { ... }

// Test BLANK  
@Test
public void shouldThrowWhenValueBlank() { ... }

// Test VALID edge case
@Test
public void shouldAcceptSingleCharacterValue() { ... }

// Test BOUNDARY
@Test
public void shouldHandleMaxLengthValue() { ... }

// Test UNICODE
@Test
public void shouldHandleUnicodeCharacters() { ... }

// Test SPECIAL CHARS
@Test
public void shouldHandleSpecialCharacters() { ... }

23. Test as Documentation¶

23.1 Reading Tests Like a Book¶

Tests MUST be written so that a reader can understand the system's expected behavior without reading source code.

@Test
public void shouldRejectEventWhenAllFiltersReject() {
    // This test documents: When multiple matchers are configured,
    // ALL must accept for the event to pass. If ANY rejects, the event is rejected.

    // arrange

    var rejectFilter1 = mock(Filter.class);
    var rejectFilter2 = mock(Filter.class);
    when(rejectFilter1.accept(anyString())).thenReturn(false);
    when(rejectFilter2.accept(anyString())).thenReturn(false);

    var route = new Route();
    route.setFilters(new Filter[] { rejectFilter1, rejectFilter2 });

    // act

    var accepted = route.accept("LOGIN");

    // assert

    assertThat(accepted)
        .as("Event should be rejected when any filter rejects")
        .isFalse();
}

23.2 Test Naming as Documentation¶

Method names describe behavior, not implementation:

//  BAD - Describes implementation
shouldCallValidateMethod()
shouldSetFieldToNull()

//  GOOD - Describes behavior
shouldRejectInvalidUrl()
shouldDefaultToTenSecondsWhenTimeoutNotSpecified()
shouldRetryThreeTimesBeforeFailingPermanently()

24. Regression Protection¶

24.1 Purpose¶

Tests exist to protect against future corruption. Every test should:

Verify a specific behavior that MUST NOT change
Fail loudly if a maintainer inadvertently breaks the contract
Provide clear error messages showing what was expected vs. what happened

24.2 Contract Verification¶

@Test
public void shouldMaintainBackwardCompatibleDefaults() {
    // This test protects the default configuration contract.
    // Changing these defaults would break existing deployments.

    // act

    var config = new Configuration();

    // assert - These are the documented defaults. DO NOT CHANGE.

    assertThat(config.isMetricsEnabled())
        .as("Metrics must be disabled by default")
        .isFalse();

    assertThat(config.getRoutes())
        .as("Routes must default to empty array")
        .isEmpty();
}

25. Checklist for Comprehensive Tests¶

25.1 Per-Test Checklist¶

[ ] Test has actual utility (not contrived)
[ ] Blank line after method opening {
[ ] // arrange with blank line before and after
[ ] // act with blank line before and after
[ ] // assert with blank line before and after
[ ] No blank line before closing }
[ ] Full state of outcome is asserted
[ ] Exact exception messages are verified
[ ] AssertJ fluent API is leveraged for expressiveness

25.2 Per-Class Checklist¶

[ ] Happy path tested
[ ] Null inputs tested
[ ] Empty inputs tested
[ ] Blank string inputs tested (where applicable)
[ ] Boundary values tested
[ ] Error conditions tested with exact messages
[ ] Tests read as documentation of expected behavior

25.3 Serializer-Specific Checklist¶

[ ] Round-trip verification (serialize → parse → compare)
[ ] All fields populated test
[ ] All fields null test
[ ] Unicode characters test
[ ] Special characters test

25.4 Destination-Specific Checklist¶

[ ] Configuration validation tests
[ ] Unconnected/unreachable broker tests
[ ] Connection failure handling tests
[ ] HTTP: MockWebServer tests for full request/response verification

Test Patterns and Conventions¶

CRITICAL RULE: ONE METHOD, ONE TEST FILE¶

CORRECT Examples:¶

INCORRECT Examples (NEVER DO THIS):¶

Rule Application:¶

DO NOT TEST: Constants, Abstract Classes, or Lombok-Generated Code¶

CRITICAL RULE: INHERITED METHODS IN IMPLEMENTATION TESTS¶

CORRECT Examples:¶

INCORRECT Examples (NEVER DO THIS):¶

Rule Application:¶

Rationale:¶

1. Directory Structure¶

1.1 Root Test Directory¶

1.2 Package Organization Pattern¶

1.3 Folder Naming Rules¶

1.4 Complete Folder Structure¶

2. File Naming¶

2.1 Pattern¶

2.2 Examples¶

2.3 Overloaded Method Naming¶

3. Package Declaration¶

3.1 Pattern¶

3.2 Standard Examples¶

3.3 Utility Class Package Convention¶

4. Imports¶

4.1 Static Imports (Always First)¶

4.2 Common Static Import Combinations¶

4.3 Regular Imports¶

5. Class Declaration¶

5.1 Class Visibility¶

5.2 Class Name¶

5.3 No Class Annotations¶

6. Test Method Declaration¶

6.1 Visibility¶

6.2 Method Naming Pattern¶

6.3 Examples by Category¶

7. Test Method Structure (AAA Pattern)¶

7.1 Required Sections¶

7.2 Standard Structure¶

7.3 Whitespace Rules (STRICT - NO EXCEPTIONS)¶

7.4 Visual Template (Copy This Exactly)¶

7.4 Section Variations¶

7.5 Cleanup Section (Rare)¶

8. Variable Declarations¶

8.1 Primary Pattern: var¶

8.2 Explicit Type Exceptions¶

8.3 Static Fields¶

9. Assertions (AssertJ)¶

9.1 Basic Assertions¶

9.2 String Assertions¶

9.3 Collection Assertions¶

9.4 Optional Assertions¶

9.5 Exception Assertions¶

9.6 Compound Boolean in Assertions¶

10. Mocking (Mockito)¶

10.1 Creating Mocks¶

10.2 Stubbing¶

10.3 Verification¶

10.4 Static Mocking¶

11. Test Data Creation¶

11.1 Inline Object Creation¶

11.2 Helper Methods¶

11.3 Private Inner Classes¶

12. Test Organization Within File¶

12.1 Logical Grouping¶

12.2 Test Order¶

13. Comments¶

13.1 Allowed Comments¶

13.2 Prohibited Comments¶

14. Exception Testing Patterns¶

14.1 Null Paramketer Tests¶

14.2 Empty/Blank String Tests¶

14.3 Exception Message Verification¶

15. Complete Test File Template¶

16. Anti-Patterns (NEVER USE)¶

17. Checklist for New Test Files¶

18. File Count by Category¶

19. Testing Philosophy & Quality Standards¶

19.1 Core Principles¶

19.2 Test Utility Requirements¶

8.1 Primary Pattern: `var`¶