Add self reference to ApplicationContextAssertProvider

[scordio]

Prior to this change, the following wouldn't compile:

new ApplicationContextRunner().run(context ->
  assertThat(context)            // returns ApplicationContextAssert<ConfigurableApplicationContext>
    .satisfies(
      ctx -> assertThat(ctx)     // returns ObjectAssert<ConfigurableApplicationContext>
        .hasNotFailed(),         // does not compile
      ctx -> assertThat(ctx)     // returns ObjectAssert<ConfigurableApplicationContext>
        .doesNotHaveBean("foo")) // does not compile
    );

This was due to ApplicationContextAssertProvider carrying ConfigurableApplicationContext as the type under assertion, which didn't play well with AssertJ methods like satisfies that allow nesting further assertions via given consumers.

Now ApplicationContextAssertProvider instances carry a self-reference, and assertions like satisfies can be chained correctly:

new ApplicationContextRunner().run(context ->
  assertThat(context)            // returns ApplicationContextAssert<AssertableApplicationContext>
    .satisfies(
      ctx -> assertThat(ctx)     // returns ApplicationContextAssert<AssertableApplicationContext>
        .hasNotFailed(),         // compiles!
      ctx -> assertThat(ctx)     // returns ApplicationContextAssert<AssertableApplicationContext>
        .doesNotHaveBean("foo")) // compiles!
    );

This is effectively a breaking change due to the additional type parameters of ApplicationContextAssertProvider. However, I imagine the change will be transparent to users who use the ApplicationContextRunner via its fluent API.

Relates to:

• Update ApplicationContextAssert to support AssertJ's soft assertions #40134 (comment)

[snicoll]

Yeah I agree that would be more idiomatic indeed. However, this is a breaking change for anyone implementing the interface so I don't think we can merge this sooner than 4.2.x. Flagging to get more feedback from the team.

[philwebb]

My vote is to wait until 4.2.x at this point. It's a nice change, but I don't want to risk accidentally breaking things this late in the release cycle.