takes_less_than(amount)equals_reference,
expect_equal_to_reference;
equals, expect_equal;
expect-compare,
expect_less_than,
expect_more_than,
is_less_than, is_more_than;
expect_equivalent,
is_equivalent_to;
expect_error, throws_error;
expect_false, expect_true,
is_false, is_true;
expect_identical,
is_identical_to; expect_is,
is_a; expect_match,
matches; expect_message,
shows_message; expect_named,
has_names; expect_null,
is_null; expect_output,
prints_text; expect_warning,
gives_warning