be matchers

There are several related “be” matchers:

  expect(obj).to be_truthy  # passes if obj is truthy (not nil or false)
  expect(obj).to be_falsey  # passes if obj is falsy (nil or false)
  expect(obj).to be_nil     # passes if obj is nil
  expect(obj).to be         # passes if obj is truthy (not nil or false)

The be_truthy matcher

Given a file named “betruthyspec.rb” with:

RSpec.describe "be_truthy matcher" do
  specify { expect(true).to be_truthy }
  specify { expect(7).to be_truthy }
  specify { expect("foo").to be_truthy }
  specify { expect(nil).not_to be_truthy }
  specify { expect(false).not_to be_truthy }

  # deliberate failures
  specify { expect(true).not_to be_truthy }
  specify { expect(7).not_to be_truthy }
  specify { expect("foo").not_to be_truthy }
  specify { expect(nil).to be_truthy }
  specify { expect(false).to be_truthy }
end

When I run rspec be_truthy_spec.rb

Then the output should contain “10 examples, 5 failures”

And the output should contain:

       expected: falsey value
            got: true

And the output should contain:

       expected: falsey value
            got: 7

And the output should contain:

       expected: falsey value
            got: "foo"

And the output should contain:

       expected: truthy value
            got: nil

And the output should contain:

       expected: truthy value
            got: false

The be_falsey matcher

Given a file named “befalseyspec.rb” with:

RSpec.describe "be_falsey matcher" do
  specify { expect(nil).to be_falsey }
  specify { expect(false).to be_falsey }
  specify { expect(true).not_to be_falsey }
  specify { expect(7).not_to be_falsey }
  specify { expect("foo").not_to be_falsey }

  # deliberate failures
  specify { expect(nil).not_to be_falsey }
  specify { expect(false).not_to be_falsey }
  specify { expect(true).to be_falsey }
  specify { expect(7).to be_falsey }
  specify { expect("foo").to be_falsey }
end

When I run rspec be_falsey_spec.rb

Then the output should contain “10 examples, 5 failures”

And the output should contain:

       expected: truthy value
            got: nil

And the output should contain:

       expected: truthy value
            got: false

And the output should contain:

       expected: falsey value
            got: true

And the output should contain:

       expected: falsey value
            got: 7

And the output should contain:

       expected: falsey value
            got: "foo"

The be_nil matcher

Given a file named “benilspec.rb” with:

RSpec.describe "be_nil matcher" do
  specify { expect(nil).to be_nil }
  specify { expect(false).not_to be_nil }
  specify { expect(true).not_to be_nil }
  specify { expect(7).not_to be_nil }
  specify { expect("foo").not_to be_nil }

  # deliberate failures
  specify { expect(nil).not_to be_nil }
  specify { expect(false).to be_nil }
  specify { expect(true).to be_nil }
  specify { expect(7).to be_nil }
  specify { expect("foo").to be_nil }
end

When I run rspec be_nil_spec.rb

Then the output should contain “10 examples, 5 failures”

And the output should contain:

       expected: not nil
            got: nil

And the output should contain:

       expected: nil
            got: false

And the output should contain:

       expected: nil
            got: true

And the output should contain:

       expected: nil
            got: 7

And the output should contain:

       expected: nil
            got: "foo"

The be matcher

Given a file named “be_spec.rb” with:

RSpec.describe "be_matcher" do
  specify { expect(true).to be }
  specify { expect(7).to be }
  specify { expect("foo").to be }
  specify { expect(nil).not_to be }
  specify { expect(false).not_to be }

  # deliberate failures
  specify { expect(true).not_to be }
  specify { expect(7).not_to be }
  specify { expect("foo").not_to be }
  specify { expect(nil).to be }
  specify { expect(false).to be }
end

When I run rspec be_spec.rb

Then the output should contain all of these:
10 examples, 5 failures
expected true to evaluate to false
expected 7 to evaluate to false
expected “foo” to evaluate to false
expected nil to evaluate to true
expected false to evaluate to true