How do You Unit Test a Custom Assert?

I'm writing my own JUnit Assert? How do I test it?

I know how to feed it something that w开发者_Python百科ill pass and something that will make it fail, but how do I write a JUnit test for those things?

The custom assert will look something like:

public static void assertSomething() {
    if (!something()) {
        fail("Expected something, but ...");
    }
}

How can I catch that fail?

fail() throws a junit.framework.AssertionFailedError, which you could catch in a unit test of your assertion method, if you like.

Example:

@Test(expected = AssertionFailedError.class)
public void testMyAssertFails() {
    assertSomething("valueThatWillFail");
}

@Test
public void testMyAssertPasses() {
    assertSomething("valueThatPasses");
    //if you reach this line, no failure was thrown
}