[timtebeek]

TestMethodsShouldBeVoid and KotlinTestMethodsShouldReturnUnit deleted every return in a test method. A guard such as if (System.getenv("SKIP") != null) { return 0; } then no longer exited, so the rest of the test ran and could fail. The recipes now only remove a return that is the last statement of the method (keeping a call like return calculate(); as calculate();), and turn every other return value; into return;:

@Test
void testMethod() {
    if (System.getenv("SKIP") != null) {
        return;
    }
    fail();
}

They leave a method unchanged when an early return's value has side effects, when it overrides another method, when it is called or referenced elsewhere in the same file (a test reused as a helper), when it has no body (previously an NPE on abstract test methods), or, in Kotlin, when a lambda returns from the test method. Returns in local classes and Kotlin local functions are no longer touched. TestMethodsShouldBeVoid also stops visiting Kotlin files, where it printed fun testMethod(): void { }.

Fixes item C4 of #1211.