Logo: Relish

  1. Sign in

Project: RSpec Expectations 3.1

Publisher: RSpec

`output` matcher

The output matcher provides a way to assert that the has emitted content to either
$stdout or $stderr.

With no arg, passes if the block outputs to_stdout or to_stderr. With a string, passes
if the blocks outputs that specific string to_stdout or to_stderr. With a regexp or
matcher, passes if the blocks outputs a string to_stdout or to_stderr that matches.

Note: This matcher works by temporarily replacing $stdout or $stderr, so it's not able
to intercept stream output that explicitly uses STDOUT/STDERR or that uses a reference
to $stdout/$stderr that was stored before the matcher is used.

Scenarios
output_to_stdout matcher
Given
a file named "output_to_stdout_spec.rb" with: 
RSpec.describe "output.to_stdout matcher" do
  specify { expect { print('foo') }.to output.to_stdout }
  specify { expect { print('foo') }.to output('foo').to_stdout }
  specify { expect { print('foo') }.to output(/foo/).to_stdout }
  specify { expect { }.to_not output.to_stdout }
  specify { expect { print('foo') }.to_not output('bar').to_stdout }
  specify { expect { print('foo') }.to_not output(/bar/).to_stdout }

  # deliberate failures
  specify { expect { }.to output.to_stdout }
  specify { expect { }.to output('foo').to_stdout }
  specify { expect { print('foo') }.to_not output.to_stdout }
  specify { expect { print('foo') }.to output('bar').to_stdout }
  specify { expect { print('foo') }.to output(/bar/).to_stdout }
end
When
I run rspec output_to_stdout_spec.rb
Then
the output should contain all of these:
11 examples, 5 failures
expected block to output to stdout, but did not
expected block to not output to stdout, but output "foo"
expected block to output "bar" to stdout, but output "foo"
expected block to output "foo" to stdout, but output nothing
expected block to output /bar/ to stdout, but output "foo"
output_to_stderr matcher
Given
a file named "output_to_stderr.rb" with: 
RSpec.describe "output_to_stderr matcher" do
  specify { expect { warn('foo') }.to output.to_stderr }
  specify { expect { warn('foo') }.to output("foo\n").to_stderr }
  specify { expect { warn('foo') }.to output(/foo/).to_stderr }
  specify { expect { }.to_not output.to_stderr }
  specify { expect { warn('foo') }.to_not output('bar').to_stderr }
  specify { expect { warn('foo') }.to_not output(/bar/).to_stderr }

  # deliberate failures
  specify { expect { }.to output.to_stderr }
  specify { expect { }.to output('foo').to_stderr }
  specify { expect { warn('foo') }.to_not output.to_stderr }
  specify { expect { warn('foo') }.to output('bar').to_stderr }
  specify { expect { warn('foo') }.to output(/bar/).to_stderr }
end
When
I run rspec output_to_stderr.rb
Then
the output should contain all of these:
11 examples, 5 failures
expected block to output to stderr, but did not
expected block to not output to stderr, but output "foo
expected block to output "bar" to stderr, but output "foo "
expected block to output "foo" to stderr, but output nothing
expected block to output /bar/ to stderr, but output "foo "

Last published over 5 years ago by myronmarston.