I suggest MyClassTests.
Classes should be noun phrases, so commonly used MyClassTest and less common MyClassTests or MyClassTestCase or MyClassTestFixture all work. Technically, an instance of a JUnit test class represents a test fixture, but TestFixture is a bit too verbose for me.
I think that MyClassTests conveys intent in the best way because there are typically multiple test methods in a class each representing a single test (test case).