Project: RSpec Mocks 3.2

Publisher: RSpec

Spies

Message expectations put an example's expectation at the start, before you've invoked the
code-under-test. Many developers prefer using an act-arrange-assert (or given-when-then)
pattern for structuring tests. Spies are an alternate type of test double that support this
pattern by allowing you to expect that a message has been received after the fact, using
have_received.

You can use any test double (or partial double) as a spy, but the double must be setup to
spy on the messages you care about. Spies automatically spy on all messages,
or you can allow a message to spy on it.

have_received supports the same fluent interface for setting constraints that normal message expectations do.

Note: The have_received API shown here will only work if you are using rspec-expectations.

Scenarios

Using a spy
Spy on a method on a partial double
Failure when the message has not been received
Set constraints using the fluent interface

Using a spy

Given

a file named "spy_spec.rb" with:

RSpec.describe "have_received" do
  it "passes when the message has been received" do
    invitation = spy('invitation')
    invitation.deliver
    expect(invitation).to have_received(:deliver)
  end
end

When

I run rspec spy_spec.rb

Then

the examples should all pass

Spy on a method on a partial double

Given

a file named "partial_double_spy_spec.rb" with:

class Invitation
  def self.deliver; end
end

RSpec.describe "have_received" do
  it "passes when the expectation is met" do
    allow(Invitation).to receive(:deliver)
    Invitation.deliver
    expect(Invitation).to have_received(:deliver)
  end
end

When

I run rspec partial_double_spy_spec.rb

Then

the examples should all pass

Failure when the message has not been received

Given

a file named "failure_spec.rb" with:

class Invitation
  def self.deliver; end
end

RSpec.describe "failure when the message has not been received" do
  example "for a spy" do
    invitation = spy('invitation')
    expect(invitation).to have_received(:deliver)
  end

  example "for a partial double" do
    allow(Invitation).to receive(:deliver)
    expect(Invitation).to have_received(:deliver)
  end
end

When

I run rspec failure_spec.rb --order defined

Then

it should fail with:

  1) failure when the message has not been received for a spy
     Failure/Error: expect(invitation).to have_received(:deliver)
       (Double "invitation").deliver(*(any args))
           expected: 1 time with any arguments
           received: 0 times with any arguments

And

it should fail with:

  2) failure when the message has not been received for a partial double
     Failure/Error: expect(Invitation).to have_received(:deliver)
       (<Invitation (class)>).deliver(*(any args))
           expected: 1 time with any arguments
           received: 0 times with any arguments

Set constraints using the fluent interface

Given

a file named "setting_constraints_spec.rb" with:

RSpec.describe "An invitiation" do
  let(:invitation) { spy("invitation") }

  before do
    invitation.deliver("[email protected]")
    invitation.deliver("[email protected]")
  end

  it "passes when a count constraint is satisfied" do
    expect(invitation).to have_received(:deliver).twice
  end

  it "passes when an order constraint is satisifed" do
    expect(invitation).to have_received(:deliver).with("[email protected]").ordered
    expect(invitation).to have_received(:deliver).with("[email protected]").ordered
  end

  it "fails when a count constraint is not satisfied" do
    expect(invitation).to have_received(:deliver).at_least(3).times
  end

  it "fails when an order constraint is not satisifed" do
    expect(invitation).to have_received(:deliver).with("[email protected]").ordered
    expect(invitation).to have_received(:deliver).with("[email protected]").ordered
  end
end

When

I run rspec setting_constraints_spec.rb --order defined

Then

it should fail with the following output:

4 examples, 2 failures

1) An invitiation fails when a count constraint is not satisfied

Failure/Error: expect(invitation).to have_received(:deliver).at_least(3).times

(Double "invitation").deliver(*(any args))

expected: at least 3 times with any arguments

received: 2 times with any arguments

2) An invitiation fails when an order constraint is not satisifed

Failure/Error: expect(invitation).to have_received(:deliver).with("[email protected]").ordered

Double "invitation" received :deliver out of order

Last published over 6 years ago by myronmarston.

Spies

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