Junit5: Parameterized Test - 'Cannot invoke non-static method' in @MethodSource with Kotlin

[AdamSHurwitz]

Expect

Convert a standard JUnit 5 test into a parameterized test in order to iterate through a stream of test cases using the @ParamterizedTest and @MethodSource annotations in Kotlin.

Observe

The @MethodSource is unable to access the stream of data. This seems to be an issue with this annotation specifically, as @ValueSource(strings = ["SF", "NYC"]) iterates through the statically defined options as expected.

Error:

PreconditionViolationException: Cannot invoke non-static method {someMethodName} on a null target.

Implement

The parameterized test is set to pass in a stream of data classes similar to the setup outlined by Phillip Hauer in Data Classes for Parameterized Tests.

Code

build.gradle (:SomeProject)

dependencies {
    ...    
    classpath("de.mannodermaus.gradle.plugins:android-junit5:$junit5_version")
}

build.gradle (:someModule)

apply plugin: "de.mannodermaus.android-junit5"
android {
    ...
    compileOptions.targetCompatibility = JavaVersion.VERSION_1_8
    kotlinOptions.jvmTarget = "1.8"
}
dependencies {
    testImplementation "org.junit.jupiter:junit-jupiter-api:5.6.2"
    testRuntimeOnly "org.junit.jupiter:junit-jupiter-engine:5.6.2"
    testImplementation "org.junit.jupiter:junit-jupiter-params:5.6.2"
}

SomeTest.kt

class SomeTest {
    private val testDispatcher = TestCoroutineDispatcher()

    private fun someDataStates() = Stream.of(
        // Kotlin data class
        TestState("123"),
        TestState("345")
    )

    @ParameterizedTest
    @MethodSource("someDataStates")
    fun someTest(testState: TestState) = testDispatcher.runBlockingTest {
        // Test state here.
        ...
    }
}

Build environment

• Android Studio 4.0
• Build #AI-193.6911.18.40.6514223, built on May 20, 2020
• Runtime version: 1.8.0_242-release-1644-b3-6222593 x86_64
• VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
• macOS 10.15.5
• GC: ParNew, ConcurrentMarkSweep
• Memory: 1979M
• Cores: 16
• Registry: ide.new.welcome.screen.force=true
• Non-Bundled Plugins: cn.wjdghd.unique.plugin.id, com.android.tool.sizereduction.plugin, com.developerphil.adbidea, com.thoughtworks.gauge, mobi.hsz.idea.gitignore

Attempted solutions

1. Refactor test case data states to a top-level function.

TestCases.kt

fun someDataStates() = Stream.of(
    TestState("123"),
    TestState("345")
)

SomeTest.kt

private fun SomeDataStates() = someDataStates()

@ParameterizedTest
@MethodSource("SomeDataStates")
fun someTest(testState: TestState) = testDispatcher.runBlockingTest {
   // Test state here.
   ...

}

2. Refactor test case data states to a top-level function of type List instead of Stream.

fun someDataStates() = listOf(
    TestState("123"),
    TestState("345")
)

Full error log

org.junit.platform.commons.PreconditionViolationException: Cannot invoke non-static method [private final {someMethodName} on a null target.
at org.junit.platform.commons.util.Preconditions.condition(Preconditions.java:296)
at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:682)
at org.junit.jupiter.params.provider.MethodArgumentsProvider.lambda$provideArguments$1(MethodArgumentsProvider.java:46)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:485)
at java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:272)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:485)
at java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:272)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:485)
at org.junit.jupiter.engine.descriptor.TestTemplateTestDescriptor.execute(TestTemplateTestDescriptor.java:106)
at org.junit.jupiter.engine.descriptor.TestTemplateTestDescriptor.execute(TestTemplateTestDescriptor.java:41)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
at java.util.ArrayList.forEach(ArrayList.java:1257)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
at java.util.ArrayList.forEach(ArrayList.java:1257)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:248)
at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$5(DefaultLauncher.java:211)
at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:226)
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:199)
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:132)
at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:69)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)
Suppressed: org.junit.platform.commons.PreconditionViolationException: Configuration error: You must configure at least one set of arguments for this @ParameterizedTest
at org.junit.platform.commons.util.Preconditions.condition(Preconditions.java:281)
at org.junit.jupiter.params.ParameterizedTestExtension.lambda$provideTestTemplateInvocationContexts$6(ParameterizedTestExtension.java:90)
at java.util.stream.AbstractPipeline.close(AbstractPipeline.java:323)
at java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:279)
... 49 more
Process finished with exit code 255

[sbrannen]

As stated in the Javadoc and User Guide documentation for @MethodSource, the referenced method must be static unless you are using @TestInstance(Lifecycle.PER_CLASS).

That is also discussed in detail in the blog you linked to.

In light of that, I am closing this issue.

If you find that you cannot make it work by properly setting the test instance lifecycle, feel free to post back additional information here.

[AdamSHurwitz]

Thank you! I forgot that Lifecycle.PER_CLASSis defined in past projects under _app/src/test/resources_ in Android Studio.

File name: _junit-platform.properties_

Code: junit.jupiter.testinstance.lifecycle.default=per_class

_See: 2.10.1 Changing the Default Test Instance Lifecycle_