its

Extracts a feature out of the current subject of this expectation with the help of the given extractor, creates a new Expect for it and returns it so that subsequent calls are based on the feature.

Extracts a feature out of the current subject of this expectation with the help of the given extractorWithCreator.extractor, creates a new Expect for it, applies an expectation-group based on the given extractorWithCreator.assertionCreator for the feature and returns the initial Expect with the current subject.

Inline property referring actually to this and allows writing infix assertions within an expectation-group

For instance, instead of:

expect {
  ...
}.toThrow<...>{
   this messageToContain "oho"
}

You can write

expect {
  ...
}.toThrow<...>{
   its messageToContain "oho"
}