testing-guide-examples.md

name	testing-guide-examples
description	Test skeleton templates for Java (JUnit 5), Scala (ScalaTest), and Kotlin (kotlin.test) in the MongoDB Java Driver. Use when writing new tests to match structural conventions.

Test Skeletons

Match these structural conventions when writing new tests.

Java — JUnit 5

public class FeatureUnderTestTest extends OperationTest {

    private ResourceType resource;

    @BeforeEach
    void setup() {
        // Insert test data, acquire resources
    }

    @AfterEach
    void cleanup() {
        // Release resources to prevent leaks
    }

    @Test
    @DisplayName("should do expected behavior")
    void shouldDoExpectedBehavior() {
        // given
        // when
        // then
    }

    @ParameterizedTest(name = "{index} => input={0}, expected={1}")
    @MethodSource
    @DisplayName("should handle varied inputs")
    void shouldHandleVariedInputs(final int input, final int expected) {
        assertEquals(expected, methodUnderTest(input));
    }

    private static Stream<Arguments> shouldHandleVariedInputs() {
        return Stream.of(arguments(1, 1), arguments(2, 4));
    }
}

Scala — ScalaTest with Mockito

class FeatureUnderTestSpec extends BaseSpec with MockitoSugar {

  val wrapped = mock[JWrappedType]
  val underTest = new ScalaWrapper(wrapped)

  "ScalaWrapper" should "have the same methods as the wrapped type" in {
    val wrappedMethods = classOf[JWrappedType].getMethods.map(_.getName).toSet
    val localMethods = classOf[ScalaWrapper].getMethods.map(_.getName)
    // Assert parity
  }

  it should "delegate to underlying method" in {
    underTest.someMethod("arg")
    verify(wrapped).someMethod("arg")
  }
}

Kotlin — kotlin.test with Mockito-Kotlin

class FeatureUnderTestTest {

    companion object {
        internal val wrapped: com.mongodb.client.MongoCollection<MyType> = mock()
        lateinit var collection: MongoCollection<MyType>

        @JvmStatic
        @BeforeAll
        internal fun setUpMocks() {
            collection = MongoCollection(wrapped)
            whenever(wrapped.namespace).doReturn(MongoNamespace("db", "coll"))
        }
    }

    @Test
    fun shouldProduceCorrectBson() {
        assertEquals(BsonDocument.parse("""{"expected": 1}"""), resultUnderTest.toBsonDocument())
    }

    data class MyType(val id: String, val name: String)
}