JUnit says my test method "could not be resolved to a unique method"

Question

Trying to learn JUnit 5 with IntelliJ IDEA. Created a test class and trying to test one method. Here's the message (see third line):

INFO: Discovered TestEngines with IDs: [junit-jupiter]
Internal Error occurred.
org.junit.platform.commons.util.PreconditionViolationException:'DirectoryTest#directory2bytes' could not be resolved to a unique method
at org.junit.platform.engine.discovery.DiscoverySelectors.lambda$selectMethod$1(DiscoverySelectors.java:131)
at java.util.Optional.orElseThrow(Optional.java:290)
at org.junit.platform.engine.discovery.DiscoverySelectors.selectMethod(DiscoverySelectors.java:130)
at com.intellij.junit5.JUnit5TestRunnerUtil.createSelector(JUnit5TestRunnerUtil.java:111)
at com.intellij.junit5.JUnit5TestRunnerUtil.buildRequest(JUnit5TestRunnerUtil.java:86)
at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:46)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:237)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Process finished with exit code 254
Empty test suite.

I can't understand why the method can't be resolved: It compiles and it's definitely there:

@Test
void directory2bytes( ) {
    testBytes = testDir.directory2bytes();
    for( int i = 0; i <= 10; i++) {
        System.out.print( testBytes[i] + " ")
    }
    System.out.println( );
}

And I have defined this:

@BeforeEach
void setUp( ) {
    testDir = new Directory( )
    testBytes = new byte[1000];
}

Update: quitting and relaunching IntelliJ IDEA, I am now getting messages that the imported symbol "junit" can't be resolved, along with the various annotations "@beforeEach", "afterEach" and "Test".

Update 2: found and fixed a missing semicolon in test class, but no change. Note: there are compile errors in some of the classes that I'm not testing, but I have the test Run configuration set to "Build, no error check". Is this right? I have also tried to create the same test (with a different class name) using JUnit 4, but that doesn't work either.

Here are first few lines of error message:

Dec 07, 2016 9:51:41 AM org.junit.platform.launcher.core.ServiceLoaderTestEngineRegistry loadTestEngines
INFO: Discovered TestEngines with IDs: [junit-jupiter, junit-vintage]
Internal Error occurred.
org.junit.platform.commons.util.PreconditionViolationException: Could not load class with name: DirectoryTest
at org.junit.platform.engine.discovery.MethodSelector.lambda$lazyLoadJavaClass$0(MethodSelector.java:154)

Answer 1

Due to a bug, M2 does not support selecting methods with parameters. This is fixed in M3. However, to use M3 in IntelliJ IDEA out of the box, you need 2016.3.1 which will be released next week. There's a workaround to use M3 with the current version of IntelliJ IDEA.