JUnit 4 to JUnit 5 Migration - COMPLETE ✅

Successfully migrated all tests in azure-spring-data-cosmos from JUnit 4 to JUnit 5 in preparation for Spring Boot 4 upgrade.

Migration Checklist

• Explore repository and understand current state
• Verify tests pass with JUnit 4 (120 tests passing)
• Update pom.xml dependencies (removed JUnit 4, removed vintage engine)
• Migrate test files (85+ files migrated)
  • Replace JUnit 4 imports with JUnit 5 equivalents
  • Update annotations (@test, @before, @after, @BeforeClass, @afterclass)
  • Update assertions (Assert.* to Assertions.*)
  • Update @RunWith annotations to @ExtendWith
  • Remove @ClassRule and @rule usage
  • Remove TestRule interface implementation
• All tests compile successfully
• Fix all test failures - convert @test(expected=...) to assertThrows
• All 120 tests passing ✅

Changes

Dependencies (pom.xml)

• Removed junit:junit 4.13.2 dependency
• Removed junit-vintage-engine compatibility layer

Test Annotations & Imports (85+ files)

• @Before/@After → @BeforeEach/@AfterEach
• @BeforeClass/@AfterClass → @BeforeAll/@AfterAll
• @Ignore → @Disabled
• @RunWith(MockitoJUnitRunner.class) → @ExtendWith(MockitoExtension.class)
• @RunWith(SpringJUnit4ClassRunner.class) → @ExtendWith(SpringExtension.class)
• org.junit.Assert → org.junit.jupiter.api.Assertions

Code Refactoring

• Removed TestRule interface implementation from AbstractIntegrationTestCollectionManager
• Removed @ClassRule and @Rule annotations
• Converted all @Test(expected=Exception.class) to assertThrows() pattern
• Fixed static imports for AssertJ and JUnit Jupiter compatibility
• Used lenient() for Mockito stubbings that are not used in all tests

Example Conversion

// Before (JUnit 4)
@Test(expected = IllegalArgumentException.class)
public void testInvalid() {
    doSomething();
}

// After (JUnit 5)
@Test
public void testInvalid() {
    assertThrows(IllegalArgumentException.class, () -> {
        doSomething();
    });
}

Test Results

✅ All 120 tests passing

• 0 failures
• 0 errors
• 0 skipped

• Fixes [FEATURE REQ] Migrate Junit4 to Jnuit5 in azure-spring-data-cosmos #47345

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