Allow JUnit rules plugin to support individually annotated tests

[ashleyfrieze]

In native JUnit, you can do something like this:

@Test
@DirtiesContext(methodMode = DirtiesContext.MethodMode.AFTER_METHOD)
public void willDoSomethingDestructiveToSpring() throws Exception {
    myBean.deleteAll();
}

The @DirtiesContext annotation is a clue to the JUnit runner or @Rule that the test method needs some variation in its treatment.

With #56 it is possible to use different mix-in objects to run JUnit rules differently in different parts of the spec. However, making a single it have different behaviour to another is not possible. This is largely because under the hood all tests appear to relate to a stub @Test public void stub() {} method.

Perhaps it would be possible to fix this by one of two ways:

// provide annotated test methods in the Mixin
public class Mixin {
   // rules stuff here

  @Test
  @InterestngAnnotation("1")
  public void interesting1() {
  }

  @Test
  @InterestngAnnotation("2")
  public void interesting2() {
  }
}

// and then in the spec refer to them

Supplier<Mixin> mixin = applyRules(Mixin.class);
describe("some suite", () -> {
  it("uses the mixin a particular way", with(methodSetup("interesting1"), () -> {
    // test something
  }));
});

An alternative is to provide the method selection when applying the rules:

Supplier<Mixin> mixin = applyRules(Mixin.class, "interesting1");
describe("some suite", () -> {
  it("uses the mixin a particular way", () -> {
    // test something
  });
});

More suggestions needed, I think.