Only enable tests that require an English locale when the locale is English

[LinkDownZ]

(project) -> assertThat(buildLog(project)).contains("invalid flag: --invalid-compiler-arg")); "Is it possible to remove the 'invalid flag:' log? The judgment may be incorrect in non-English locales."

[wilkinsona]

I think we have some other tests that also assume an English locale, such as those that expect a PortInUseException to be thrown.

How do you deal with this @bclozel, @mhalbritter, and @snicoll?

[bclozel]

I'm using an English locale...

[mhalbritter]

I've ran our main branch with a de_DE locale, and got this build scan:

https://ge.spring.io/s/6ewqquhhxvln4

When looking at the failures:

• 2x times this problem
• 6x PortInUseException is not thrown if system language is not english #29918
• 1x Elasticsearch which expected "Connection refused" but got the German equivalent

[wilkinsona]

We discussed this today and decided that we're going to introduce @EnabledOnLocale in spring-boot-test-support and annotate the affected tests so that they only run when the locale's language is English – perhaps something like @EnabledOnLocale(language = "en").