java.lang.Exception: No runnable methods exception in running JUnits

You will get this exception, if you use the JUnit 4.4 core runner to execute a class that has no "@Test" method. Kindly consult the link for more info.

courtesy vipin8169

In my case I had wrong package imported:

import org.testng.annotations.Test;

instead of

import org.junit.Test;

Beware of your ide autocomplete.

My controller test in big shortcut:

@RunWith(SpringRunner.class)
@SpringBootTest
public class TaskControllerTest {
   //...
   //tests
   //
}

I just removed "public" and magically it worked.

This solution will apply to a very small percentage of people, typically people implementing their own JUnit test runners and using a separate ClassLoader.

This can happen when you load a class from a different ClassLoader, then attempt to run that test from an instance of JUnitCore loaded from the system class loader. Example:

// Load class
URLClassLoader cl = new URLClassLoader(myTestUrls, null);
Class<?>[] testCls = cl.loadClass("com.gubby.MyTest");

// Run test
JUnitCore junit = new JUnitCore();
junit.run(testCls); // Throws java.lang.Exception: No runnable methods

Looking at the stack trace:

java.lang.Exception: No runnable methods
at org.junit.runners.BlockJUnit4ClassRunner.validateInstanceMethods(BlockJUnit4ClassRunner.java:169)
at org.junit.runners.BlockJUnit4ClassRunner.collectInitializationErrors(BlockJUnit4ClassRunner.java:104)
at org.junit.runners.ParentRunner.validate(ParentRunner.java:355)
at org.junit.runners.ParentRunner.<init>(ParentRunner.java:76)
at org.junit.runners.BlockJUnit4ClassRunner.<init>(BlockJUnit4ClassRunner.java:57)
at org.junit.internal.builders.JUnit4Builder.runnerForClass(JUnit4Builder.java:10)
at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59)
at org.junit.internal.builders.AllDefaultPossibilitiesBuilder.runnerForClass(AllDefaultPossibilitiesBuilder.java:26)
at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59)
at org.junit.internal.requests.ClassRequest.getRunner(ClassRequest.java:26)
at org.junit.runner.JUnitCore.run(JUnitCore.java:138)

The problem actually occurs at BlockJUnit4ClassRunner:169 (assuming JUnit 4.11):

https://github.com/junit-team/junit/blob/r4.11/src/main/java/org/junit/runners/BlockJUnit4ClassRunner.java#L95

Where it checks which methods are annotated with @Test:

protected List<FrameworkMethod> computeTestMethods() {
    return getTestClass().getAnnotatedMethods(Test.class);
}

In this case, Test.class will have been loaded with the system ClassLoader (i.e. the one that loaded JUnitCore), therefore technically none of your test methods will have been annotated with that annotation.

Solution is to load JUnitCore in the same ClassLoader as the tests themselves.

---

Edit: In answer to the question from user3486675, you need to create a ClassLoader that doesn't delegate to the system class loader, e.g.:

private static final class IsolatedURLClassLoader extends URLClassLoader {
    private IsolatedURLClassLoader(URL[] urls) {
        // Prevent delegation to the system class loader.
        super(urls, null);
    }
}

Pass this a set of URLs that includes everything you need. You can create this by filtering the system classpath. Note that you cannot simply delegate to the parent ClassLoader, because those classes would then get loaded by that rather than the ClassLoader of your test classes.

Then you need to kick off the whole JUnit job from a class loaded by this ClassLoader. It gets messy here. Something like this utter filth below:

public static final class ClassLoaderIsolatedTestRunner {

    public ClassLoaderIsolatedTestRunner() {
        // Disallow construction at all from wrong ClassLoader
        ensureLoadedInIsolatedClassLoader(this);
    }

    // Do not rename.
    public void run_invokedReflectively(List<String> testClasses) throws BuildException {
        // Make sure we are not accidentally working in the system CL
        ensureLoadedInIsolatedClassLoader(this);

        // Load classes
        Class<?>[] classes = new Class<?>[testClasses.size()];
        for (int i=0; i<testClasses.size(); i++) {
            String test = testClasses.get(i);
            try {
                classes[i] = Class.forName(test);
            } catch (ClassNotFoundException e) {
                String msg = "Unable to find class file for test ["+test+"]. Make sure all " +
                        "tests sources are either included in this test target via a 'src' " +
                        "declaration.";
                throw new BuildException(msg, e);
            }
        }

        // Run
        JUnitCore junit = new JUnitCore();
        ensureLoadedInIsolatedClassLoader(junit);
        junit.addListener(...);
        junit.run(classes);
    }

    private static void ensureLoadedInIsolatedClassLoader(Object o) {
        String objectClassLoader = o.getClass().getClassLoader().getClass().getName();

        // NB: Can't do instanceof here because they are not instances of each other.
        if (!objectClassLoader.equals(IsolatedURLClassLoader.class.getName())) {
            throw new IllegalStateException(String.format(
                    "Instance of %s not loaded by a IsolatedURLClassLoader (loaded by %s)",
                    cls, objectClassLoader));
        }
    }
}

THEN, you need to invoke the runner via reflection:

Class<?> runnerClass = isolatedClassLoader.loadClass(ClassLoaderIsolatedTestRunner.class.getName());

// Invoke via reflection (List.class is OK because it just uses the string form of it)
Object runner = runnerClass.newInstance();
Method method = runner.getClass().getMethod("run_invokedReflectively", List.class);
method.invoke(...);