[9.x] Improve test failure output

[jessarcher]

In #38025 and #38046, we improved the test output for the assertStatus methods to display any exceptions or errors that may have caused the status assertion to fail.

These improvements almost removed the need to call withoutExceptionHandling. Almost...

This PR expands on the previous work to display exceptions or errors on any failed assertion, not just status assertions, and not even just TestResponse assertions.

A common example is when asserting Inertia redirects, and an unexpected validation error occurs. The current output doesn't give any clues that the redirect assertion failure was due to a validation error:

Under the hood, this calls assertStatus and assertLocation, but it's only the assertLocation that fails, which doesn't currently display exceptions or errors.

With the changes in this PR, the error now looks like this:

Note Unfortunately, it doesn't seem possible to inject the exception/error after the ComparisonFailure diff, so the output is not 100% what I'd want.

The existing assertStatus behaviour is now handled by this new logic, so there's no duplication of code. There is a minor change in output because the extra content is now appended after PHPUnit's raw assertion error instead of before it:

Before:

After:

We'll now also see this extra context even if we don't assert against the TestResponse. For example, imagine this test where we expect a user record to be created:

$this->post('/users', []);

$this->assertSame(1, User::count());

If a validation error or exception occurred during the last request, we'll get the extra context on PHPUnit's built-in assertions like assertSame:

The only scenario I can think of where this feature is undesirable is the assertJson assertion. If a validation error occurs, the assertJson assertion will already show the full response body. To prevent duplicate output, I've ensured that we don't append the JSON error response if the existing message already includes it.

If the user makes multiple requests in one test, only errors/exceptions from the latest request will be displayed, hopefully preventing red herrings.

The extra context will only be displayed when an assertion fails, so you won't see any output if you expect an error or exception as long as your assertions pass.

Developers may opt-out of this feature by overriding the onNotSuccessfulTest method in their base test case to throw the given exception like PHPUnit does by default.

[jbrooksuk]

@jessarcher you may have put EOF where it is for indentation, so feel free to ignore this.

[jessarcher]

@nunomaduro I'd appreciate your thoughts on this one.

Do you see any issues hooking into onNotSuccessfulTest and appending to the message property on ExpectationFailedException exceptions?

Would this feature also be beneficial for Pest or can you think of any issues it might cause?

[taylorotwell]

@jessarcher marking as draft until we get feedback from @nunomaduro

[nunomaduro]

Does this works? Asking because it seems we change the format of the JSON string by using the JSON_PRETTY_PRINT flag.

[jessarcher]

Yeah - the existing output in the exception is also pretty printed

[nunomaduro]

@jessarcher I've rebased, added minor changes, and made a few comments. Generally, this pull request seems OK to me. In addition, I've tested this pull request against Vapor test suite - more than 600 test cases - and seems to be all working.