Implement send_email matcher

features/matchers/send_email_matcher.feature

@@ -0,0 +1,68 @@
+Feature: `send_email` matcher
+
+  The `send_email` matcher is used to check if an email with the given parameters has been sent inside the expectation block.
+
+  NOTE: It implies that the spec example actually sends the email using the test adapter and does not schedule it for background.
+
+  To have an email sent in tests make sure:
+  - `ActionMailer` performs deliveries - `Rails.application.config.action_mailer.perform_deliveries = true`
+  - If the email is sent asynchronously (with `.deliver_later` call), ActiveJob uses the inline adapter - `Rails.application.config.active_job.queue_adapter = :inline`
+  - ActionMailer uses the test adapter - `Rails.application.config.action_mailer.delivery_method = :test`
+
+  If you want to check an email has been scheduled for background, use the `have_enqueued_email` matcher.
+
+  Scenario: Checking email sent with the given multiple parameters
+    Given a file named "spec/mailers/notifications_mailer_spec.rb" with:
+      """ruby
+      require "rails_helper"
+
+      RSpec.describe NotificationsMailer do
+        it "checks email sending by multiple params" do
+          expect {
+            NotificationsMailer.signup.deliver_now
+          }.to send_email(
+            from: '[email protected]',
+            to: '[email protected]',
+            subject: 'Signup'
+          )
+        end
+      end
+      """
+    When I run `rspec spec/mailers/notifications_mailer_spec.rb`
+    Then the examples should all pass
+
+  Scenario: Checking email sent with matching parameters
+    Given a file named "spec/mailers/notifications_mailer_spec.rb" with:
+      """ruby
+      require "rails_helper"
+
+      RSpec.describe NotificationsMailer do
+        it "checks email sending by one param only" do
+          expect {
+            NotificationsMailer.signup.deliver_now
+          }.to send_email(
+            to: '[email protected]'
+          )
+        end
+      end
+      """
+    When I run `rspec spec/mailers/notifications_mailer_spec.rb`
+    Then the examples should all pass
+
+  Scenario: Checking email not sent with the given parameters
+    Given a file named "spec/mailers/notifications_mailer_spec.rb" with:
+      """ruby
+      require "rails_helper"
+
+      RSpec.describe NotificationsMailer do
+        it "checks email not sent" do
+          expect {
+            NotificationsMailer.signup.deliver_now
+          }.to_not send_email(
+            to: '[email protected]'
+          )
+        end
+      end
+      """
+    When I run `rspec spec/mailers/notifications_mailer_spec.rb`
+    Then the examples should all pass

lib/rspec/rails/matchers.rb

@@ -20,6 +20,7 @@ module Matchers
 require 'rspec/rails/matchers/relation_match_array'
 require 'rspec/rails/matchers/be_valid'
 require 'rspec/rails/matchers/have_http_status'
+require 'rspec/rails/matchers/send_email'
 
 if RSpec::Rails::FeatureCheck.has_active_job?
   require 'rspec/rails/matchers/active_job'

lib/rspec/rails/matchers/send_email.rb

@@ -0,0 +1,122 @@
+# frozen_string_literal: true
+
+module RSpec
+  module Rails
+    module Matchers
+      # @api private
+      #
+      # Matcher class for `send_email`. Should not be instantiated directly.
+      #
+      # @see RSpec::Rails::Matchers#send_email
+      class SendEmail < RSpec::Rails::Matchers::BaseMatcher
+        # @api private
+        # Define the email attributes that should be included in the inspection output.
+        INSPECT_EMAIL_ATTRIBUTES = %i[subject from to cc bcc].freeze
+
+        def initialize(criteria)
+          @criteria = criteria
+        end
+
+        # @api private
+        def supports_value_expectations?
+          false
+        end
+
+        # @api private
+        def supports_block_expectations?
+          true
+        end
+
+        def matches?(block)
+          define_matched_emails(block)
+
+          @matched_emails.one?
+        end
+
+        # @api private
+        # @return [String]
+        def failure_message
+          result =
+            if multiple_match?
+              "More than 1 matching emails were sent."
+            else
+              "No matching emails were sent."
+            end
+          "#{result}#{sent_emails_message}"
+        end
+
+        # @api private
+        # @return [String]
+        def failure_message_when_negated
+          "Expected not to send an email but it was sent."
+        end
+
+        private
+
+        def diffable?
+          true
+        end
+
+        def deliveries
+          ActionMailer::Base.deliveries
+        end
+
+        def define_matched_emails(block)
+          before = deliveries.dup
+
+          block.call
+
+          after = deliveries
+
+          @diff = after - before
+          @matched_emails = @diff.select(&method(:matched_email?))
+        end
+
+        def matched_email?(email)
+          @criteria.all? do |attr, value|
+            expected =
+              case attr
+              when :to, :from, :cc, :bcc then Array(value)
+              else
+                value
+              end
+
+            values_match?(expected, email.public_send(attr))
+          end
+        end
+
+        def multiple_match?
+          @matched_emails.many?
+        end
+
+        def sent_emails_message
+          if @diff.empty?
+            "\n\nThere were no any emails sent inside the expectation block."
+          else
+            sent_emails =
+              @diff.map do |email|
+                inspected = INSPECT_EMAIL_ATTRIBUTES.map { |attr| "#{attr}: #{email.public_send(attr)}" }.join(", ")
+                "- #{inspected}"
+              end.join("\n")
+            "\n\nThe following emails were sent:\n#{sent_emails}"
+          end
+        end
+      end
+
+      # @api public
+      # Check email sending with specific parameters.
+      #
+      # @example Positive expectation
+      #   expect { action }.to send_email
+      #
+      # @example Negative expectations
+      #   expect { action }.not_to send_email
+      #
+      # @example More precise expectation with attributes to match
+      #   expect { action }.to send_email(to: '[email protected]', subject: 'Confirm email')
+      def send_email(criteria = {})
+        SendEmail.new(criteria)
+      end
+    end
+  end
+end

spec/rspec/rails/matchers/send_email_spec.rb

@@ -0,0 +1,168 @@
+RSpec.describe "send_email" do
+  let(:mailer) do
+    Class.new(ActionMailer::Base) do
+      self.delivery_method = :test
+
+      def test_email
+        mail(
+          from: "[email protected]",
+          cc: "[email protected]",
+          bcc: "[email protected]",
+          to: "[email protected]",
+          subject: "Test email",
+          body: "Test email body"
+        )
+      end
+    end
+  end
+
+  it "checks email sending by all params together" do
+    expect {
+      mailer.test_email.deliver_now
+    }.to send_email(
+      from: "[email protected]",
+      to: "[email protected]",
+      cc: "[email protected]",
+      bcc: "[email protected]",
+      subject: "Test email",
+      body: a_string_including("Test email body")
+    )
+  end
+
+  it "checks email sending by no params" do
+    expect {
+      mailer.test_email.deliver_now
+    }.to send_email
+  end
+
+  it "with to_not" do
+    expect {
+      mailer.test_email.deliver_now
+    }.to_not send_email(
+      from: "[email protected]"
+    )
+  end
+
+  it "fails with a clear message" do
+    expect {
+      expect { mailer.test_email.deliver_now }.to send_email(from: '[email protected]')
+    }.to raise_error(RSpec::Expectations::ExpectationNotMetError, <<~MSG.strip)
+      No matching emails were sent.
+
+      The following emails were sent:
+      - subject: Test email, from: ["[email protected]"], to: ["[email protected]"], cc: ["[email protected]"], bcc: ["[email protected]"]
+    MSG
+  end
+
+  it "fails with a clear message when no emails were sent" do
+    expect {
+      expect { }.to send_email
+    }.to raise_error(RSpec::Expectations::ExpectationNotMetError, <<~MSG.strip)
+      No matching emails were sent.
+
+      There were no any emails sent inside the expectation block.
+    MSG
+  end
+
+  it "fails with a clear message for negated version" do
+    expect {
+      expect { mailer.test_email.deliver_now }.to_not send_email(from: "[email protected]")
+    }.to raise_error(RSpec::Expectations::ExpectationNotMetError, "Expected not to send an email but it was sent.")
+  end
+
+  it "fails for multiple matches" do
+    expect {
+      expect { 2.times { mailer.test_email.deliver_now } }.to send_email(from: "[email protected]")
+    }.to raise_error(RSpec::Expectations::ExpectationNotMetError, <<~MSG.strip)
+      More than 1 matching emails were sent.
+
+      The following emails were sent:
+      - subject: Test email, from: ["[email protected]"], to: ["[email protected]"], cc: ["[email protected]"], bcc: ["[email protected]"]
+      - subject: Test email, from: ["[email protected]"], to: ["[email protected]"], cc: ["[email protected]"], bcc: ["[email protected]"]
+    MSG
+  end
+
+  context "with compound matching" do
+    it "works when both matchings pass" do
+      expect {
+        expect {
+          mailer.test_email.deliver_now
+        }.to send_email(to: "[email protected]").and send_email(from: "[email protected]")
+      }.to_not raise_error
+    end
+
+    it "works when first matching fails" do
+      expect {
+        expect {
+          mailer.test_email.deliver_now
+        }.to send_email(to: "[email protected]").and send_email(to: "[email protected]")
+      }.to raise_error(RSpec::Expectations::ExpectationNotMetError, <<~MSG.strip)
+        No matching emails were sent.
+
+        The following emails were sent:
+        - subject: Test email, from: ["[email protected]"], to: ["[email protected]"], cc: ["[email protected]"], bcc: ["[email protected]"]
+      MSG
+    end
+
+    it "works when second matching fails" do
+      expect {
+        expect {
+          mailer.test_email.deliver_now
+        }.to send_email(to: "[email protected]").and send_email(to: "[email protected]")
+      }.to raise_error(RSpec::Expectations::ExpectationNotMetError, <<~MSG.strip)
+        No matching emails were sent.
+
+        The following emails were sent:
+        - subject: Test email, from: ["[email protected]"], to: ["[email protected]"], cc: ["[email protected]"], bcc: ["[email protected]"]
+      MSG
+    end
+  end
+
+  context "with a custom negated version defined" do
+    define_negated_matcher :not_send_email, :send_email
+
+    it "works with a negated version" do
+      expect {
+        mailer.test_email.deliver_now
+      }.to not_send_email(
+        from: "[email protected]"
+      )
+    end
+
+    it "fails with a clear message" do
+      expect {
+        expect { mailer.test_email.deliver_now }.to not_send_email(from: "[email protected]")
+      }.to raise_error(RSpec::Expectations::ExpectationNotMetError, "Expected not to send an email but it was sent.")
+    end
+
+    context "with a compound negated version" do
+      it "works when both matchings pass" do
+        expect {
+          expect {
+            mailer.test_email.deliver_now
+          }.to not_send_email(to: "[email protected]").and not_send_email(from: "[email protected]")
+        }.to_not raise_error
+      end
+
+      it "works when first matching fails" do
+        expect {
+          expect {
+            mailer.test_email.deliver_now
+          }.to not_send_email(to: "[email protected]").and send_email(to: "[email protected]")
+        }.to raise_error(RSpec::Expectations::ExpectationNotMetError, a_string_including(<<~MSG.strip))
+          Expected not to send an email but it was sent.
+        MSG
+      end
+
+      it "works when second matching fails" do
+        expect {
+          expect {
+            mailer.test_email.deliver_now
+          }.to send_email(to: "[email protected]").and not_send_email(to: "[email protected]")
+        }.to raise_error(RSpec::Expectations::ExpectationNotMetError, a_string_including(<<~MSG.strip))
+          Expected not to send an email but it was sent.
+        MSG
+      end
+    end
+  end
+end