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Feature: Define negated matcher
You can use `RSpec::Matchers.define_negated_matcher` to define a negated version of
an existing matcher. This is particularly useful in composed matcher expressions.
@skip-when-ripper-unsupported
Scenario: Composed negated matcher expression
Given a file named "composed_negated_expression_spec.rb" with:
"""ruby
RSpec::Matchers.define_negated_matcher :an_array_excluding, :include
RSpec.describe "A negated matcher" do
let(:list) { 1.upto(10).to_a }
it "can be used in a composed matcher expression" do
expect { list.delete(5) }.to change { list }.to(an_array_excluding 5)
end
it "provides a good failure message based on the name" do
# deliberate failure
expect { list.delete(1) }.to change { list }.to(an_array_excluding 5)
end
end
"""
When I run `rspec composed_negated_expression_spec.rb`
Then the output should contain all of these:
| 2 examples, 1 failure |
| 1) A negated matcher provides a good failure message based on the name |
| Failure/Error: expect { list.delete(1) }.to change { list }.to(an_array_excluding 5) |
| expected `list` to have changed to an array excluding 5, but is now [2, 3, 4, 5, 6, 7, 8, 9, 10] |
|
