modify testCheckArgument_simpleMessage_failure to clean code

[intonormal]

verifySimpleMessage(expected) change to assertThat(expected).hasMessage("A message"),

so that the compared target("A message") can be saw straightway

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[intonormal]

I signed it!
this is my first contribute in open source
exciting and hope to be accepted

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CLAs look good, thanks!

[cpovirk]

Sorry that we sat on this (and so many pull requests) for so long.

If "A message" appeared inline in the setup for the test, I would agree that there's a clear benefit to including it inline in the assertion. But it's already defined elsewhere, so this test already fails to be readable on its own :( You could probably fine a way to move all the information inline if you want, but I'd encourage you to look for something more substantial. Maybe #2394 if you're still interested.