Equality matchers

Ruby exposes several different methods for handling equality:

a.equal?(b) # object identity - a and b refer to the same object a.eql?(b) # object equivalence - a and b have the same value a == b # object equivalence - a and b have the same value with type conversions

Note that these descriptions are guidelines but are not forced by the language. Any object can implement any of these methods with its own semantics.

rspec-expectations ships with matchers that align with each of these methods:

expect(a).to equal(b) # passes if a.equal?(b)
expect(a).to eql(b)   # passes if a.eql?(b)
expect(a).to be == b  # passes if a == b

It also ships with two matchers that have more of a DSL feel to them:

expect(a).to be(b) # passes if a.equal?(b)
expect(a).to eq(b) # passes if a == b

Compare using eq (==)

Given a file named "compare_using_eq.rb" with:

RSpec.describe "a string" do
  it "is equal to another string of the same value" do
    expect("this string").to eq("this string")
  end

  it "is not equal to another string of a different value" do
    expect("this string").not_to eq("a different string")
  end
end

RSpec.describe "an integer" do
  it "is equal to a float of the same value" do
    expect(5).to eq(5.0)
  end
end

When I run rspec compare_using_eq.rb

Then the output should contain "3 examples, 0 failures".

Compare using ==

Given a file named "compare_using_==.rb" with:

RSpec.describe "a string" do
  it "is equal to another string of the same value" do
    expect("this string").to be == "this string"
  end

  it "is not equal to another string of a different value" do
    expect("this string").not_to be == "a different string"
  end
end

RSpec.describe "an integer" do
  it "is equal to a float of the same value" do
    expect(5).to be == 5.0
  end
end

When I run rspec compare_using_==.rb

Then the output should contain "3 examples, 0 failures".

Compare using eql (eql?)

Given a file named "compare_using_eql.rb" with:

RSpec.describe "an integer" do
  it "is equal to another integer of the same value" do
    expect(5).to eql(5)
  end

  it "is not equal to another integer of a different value" do
    expect(5).not_to eql(6)
  end

  it "is not equal to a float of the same value" do
    expect(5).not_to eql(5.0)
  end

end

When I run rspec compare_using_eql.rb

Then the output should contain "3 examples, 0 failures".

Compare using equal (equal?)

Given a file named "compare_using_equal.rb" with:

RSpec.describe "a string" do
  it "is equal to itself" do
    string = "this string"
    expect(string).to equal(string)
  end

  it "is not equal to another string of the same value" do
    expect("this string").not_to equal("this string")
  end

  it "is not equal to another string of a different value" do
    expect("this string").not_to equal("a different string")
  end

end

When I run rspec compare_using_equal.rb

Then the output should contain "3 examples, 0 failures".

Compare using be (equal?)

Given a file named "compare_using_be.rb" with:

RSpec.describe "a string" do
  it "is equal to itself" do
    string = "this string"
    expect(string).to be(string)
  end

  it "is not equal to another string of the same value" do
    expect("this string").not_to be("this string")
  end

  it "is not equal to another string of a different value" do
    expect("this string").not_to be("a different string")
  end

end

When I run rspec compare_using_be.rb

Then the output should contain "3 examples, 0 failures".