AssertThrowsMinimizer
Minimize the amount of logic in assertThrows

The problem

Prefer to minimize the amount of logic in a lambda passed to assertThrows.

An assertThrows assertion will pass if any code in the provided lambda throws the given exception. If the lambda contains multiple expressions that may throw, the test may incorrectly pass if an earlier expression unexpectedly throws. For example, consider:

assertThrows(
    IllegalArgumentException.class,
    () ->
        EncodingUtil.convertAudioFormatToMp3Configuration(
            AudioEncoding.newBuilder()
                .setAudioFormat(AudioFormat.AUDIO_FORMAT_MP3)
                .setAudioQuality(AudioQuality.UNRECOGNIZED)
                .build()));

This assertion is intended to check that convertAudioFormatToMp3Configuration() throws IllegalArgumentException, but the assertion will always pass because the setup logic in setAudioQuality(AudioQuality.UNRECOGNIZED) is incorrect and build() will throw IllegalArgumentException.

Instead, you should minimize the amount of logic inside of your assertThrows:

AudioEncoding audioEncoding =
    AudioEncoding.newBuilder()
        .setAudioFormat(AudioFormat.AUDIO_FORMAT_MP3)
        .setAudioQuality(AudioQuality.UNRECOGNIZED) // BOOM goes the dynamite!
        .build();
assertThrows(
    IllegalArgumentException.class,
    () -> EncodingUtil.convertAudioFormatToMp3Configuration(audioEncoding));

The test above now (correctly) fails and exposes the setup issue.

Variable types and names

This check tries to pick a reasonable name for the extracted variable, but there may be a better name. If the extracted variable seems verbose, consider renaming it to improve readability.

In some cases a judicious use of var could improve readability, following the guidelines for usage of var.

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("AssertThrowsMinimizer") to the enclosing element.