Short text about the matcher's purpose. This explains what condition satisfies the matcher. The description is used when the one-liner syntax is used.

it { is_expected.to do_something }

The phrasing should be such that it reads "it ___." where the blank is what is returned by this method.

Message displayed when the matcher isn't satisifed.

This is only called when #match? returns false.

The message should typically only contain the test expression labels. Actual values should be returned by #values.

Checks whether the matcher is satisifed with the expression given to it.

Additional information about the match failure when negated.

By default, just the actual value is produced (same as #values). The return value must be a NamedTuple with Strings for each value. The tuple can be of any size, but the keys must be known at compile-time (as Symbols), and the values must be strings. Generally, the string values are produced by calling #inspect on the relevant object. It should look like this:

{
  expected: "Not foo",
  actual:   "bar",
}

The values should typically only contain the test expression values, not the labels. Labeled should be returned by #failure_message_when_negated.

Additional information about the match failure.

By default, just the actual value is produced. The return value must be a NamedTuple with Strings for each value. The tuple can be of any size, but the keys must be known at compile-time (as Symbols), and the values must be strings. Generally, the string values are produced by calling #inspect on the relevant object. It should look like this:

{
  expected: "foo",
  actual:   "bar",
}

The values should typically only contain the test expression values, not the labels. Labeled should be returned by #failure_message.