Formatting output so that Intellij Idea shows diffs for two texts

IntelliJ IDEA is using the hardcoded regular expression. If the text matches the pattern, it will suggest to click to view the difference.

The pattern is:

expected:<bla-blah> but was:<blah-blah-blah>

Output should match the format of assertEquals or assertThat.

The exact patterns are somewhat scattered around the code in IDEA, but some are e.g. here.

I had the same Problem and found the solution in https://github.com/joel-costigliola/assertj-core/issues/1364#issuecomment-440800958

You should throw an org.junit.ComparisonFailure. Then IntelliJ will display the <Click to see difference>