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RSpec.shared_examples "an RSpec value matcher" do |options|
let(:valid_value) { options.fetch(:valid_value) }
let(:invalid_value) { options.fetch(:invalid_value) }
matcher :always_passes do
match { |_actual| true }
end
matcher :always_fails do
match { |_actual| false }
end
def valid_expectation
expect(valid_value)
end
def invalid_expectation
expect(invalid_value)
end
include_examples "an RSpec matcher", options
it 'preserves the symmetric property of `==`' do
expect(matcher).to eq(matcher)
expect(matcher).not_to eq(valid_value)
expect(valid_value).not_to eq(matcher)
end
it 'matches a valid value when using #=== so it can be composed' do
expect(matcher).to be === valid_value
end
it 'does not match an invalid value when using #=== so it can be composed' do
expect(matcher).not_to be === invalid_value
end
it 'can be used in a composed matcher expression' do
expect([valid_value, invalid_value]).to include(matcher)
expect {
expect([invalid_value]).to include(matcher)
}.to fail_including("include (#{matcher.description})")
end
it 'uses the `ObjectFormatter` for `failure_message`' do
allow(RSpec::Support::ObjectFormatter).to receive(:format).and_return("detailed inspect")
matcher.matches?(invalid_value)
message = matcher.failure_message
# Undo our stub so it doesn't affect the `include` matcher below.
allow(RSpec::Support::ObjectFormatter).to receive(:format).and_call_original
expect(message).to include("detailed inspect")
end
it 'fails when given a block' do
expect {
expect { 2 + 2 }.to matcher
}.to fail_with(/must pass an argument rather than a block/)
unless options[:disallows_negation]
expect {
expect { 2 + 2 }.not_to matcher
}.to fail_with(/must pass an argument rather than a block/)
end
end
end
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