Android JUnit Testing … How to Expect an Exception

Question

I\'m attempting to write some tests using the built-in android Junit testing framework. I am running into a problem with a test where I am expecting an exception to be thrown.

Answer 1

I've been looking for some good solutions, however, none of the solutions was really satisfying to me. So, I created my own.

public final void assertThrows(VoidFunction v, Class e) {
    try {
        v.call();
    } catch (Exception ex) {
        if (!ex.getClass().equals(e)) {
            Assert.fail();
        }
        // Do nothing, basically succeeds test if same exception was thrown.
        return;
    }

    // Fails if no exception is thrown by default.
    Assert.fail();
}

Where VoidFunction is a simple interface:

@FunctionalInterface
public interface VoidFunction {
    void call();
}

This is used as follows (for example):

@Test
public void testFoo() {
    assertThrows(() -> foo.bar(null)), NullPointerException.class);
    assertThrows(() -> foo.setPositiveInt(-5)), IllegalArgumentException.class);
    assertThrows(() -> foo.getObjectAt(-100)), IndexOutOfBoundsException.class);
    assertThrows(new VoidFunction() {
            @Override
            public void call() {
                foo.getObjectAt(-100);
            }
        }, IndexOutOfBoundsException.class); // Success
    assertThrows(new VoidFunction() {
                @Override
                public void call() {
                    throw new Exception();
                }
            }, NullPointerException.class); // Fail

}

I included one call without using the lambda, this makes it easier to understand code sometimes, at least for me. Simple to use and it allows multiple exception catches in ONE method.