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Defining a matcher outside rspec

You can define custom matchers when using rspec-expectations outside of rspec-core.

Define a matcher with default messages​

Given a file named "test_multiples.rb" with:

require "minitest/autorun"
require "rspec/expectations/minitest_integration"

RSpec::Matchers.define :be_a_multiple_of do |expected|
  match do |actual|
    actual % expected == 0
  end
end

class TestMultiples < Minitest::Test

  def test_9_should_be_a_multiple_of_3
    expect(9).to be_a_multiple_of(3)
  end

  def test_9_should_be_a_multiple_of_4
    expect(9).to be_a_multiple_of(4)
  end

end

When I run ruby test_multiples.rb

Then the exit status should not be 0

And the output should contain "expected 9 to be a multiple of 4"

And the output should contain "2 runs, 2 assertions, 1 failures, 0 errors".