[prone] Apply UnnecessaryLambda

[Pankraz76]

• UnusedMethod not recognize Junit MethodSource google/error-prone#5289

ReturnValueIgnored:

  Did you mean 'final class EncodingTest extends GradleIntegrationHarness {'?
/Users/vincent.potucek/IdeaProjects/spotless/plugin-gradle/src/test/java/com/diffplug/gradle/spotless/EncodingTest.java:54: error: [ReturnValueIgnored] Return value of 'contains' must be used
                gradleRunner().withArguments("spotlessApply").buildAndFail().getOutput().contains("Encoding error!");
                                                                                                 ^
    (see https://errorprone.info/bugpattern/ReturnValueIgnored)
  Did you mean 'assertThat(gradleRunner().withArguments("spotlessApply").buildAndFail().getOutput().contains("Encoding error!")).isTrue();' or 'var unused = gradleRunner().withArguments("spotlessApply").buildAndFail().getOutput().contains("Encoding error!");' or to remove this line?
/Users/vincent.potucek/IdeaProjects/spotless/plugin-gradle/src/test/java/com/diffplug/gradle/spotless/EncodingTest.java:78: error: [ReturnValueIgnored] Return value of 'contains' must be used
                gradleRunner().withArguments("spotlessApply").buildAndFail().getOutput().contains("Encoding error!");
                                                                                                 ^
    (see https://errorprone.info/bugpattern/ReturnValueIgnored)
  Did you mean 'assertThat(gradleRunner().withArguments("spotlessApply").buildAndFail().getOutput().contains("Encoding error!")).isTrue();' or 'var unused = gradleRunner().withArguments("spotlessApply").buildAndFail().getOutput().contains("Encoding error!");' or to remove this line?

[Pankraz76]

now its working as we have enabled convention. the warnings does not break the build somehow.

[Pankraz76]

too much risk and too big. Some extension maven stuff might be unused in code but break on production.

[Pankraz76]

use or loose. Should we check this or adapt the test by removing or inverting this?

Should we extract the ReturnValueIgnored recipe?

[nedtwigg]

I am baffled by this one. The old test was wrong, but the new one looks wrong too. It would be nice to make this test better while we're in here, but I don't want it to hold up the rest.