Easier feature flag handling for Cypress (#16379)

* Add RailsEnvConstraint for routes

* Add feature flags API

* Add Cypress commands

* Add show action, update commands, add e2e test

* Update cypress/integration/seededFlows/toggleFeatureFlags.spec.js

Co-authored-by: Suzanne Aitchison <suzanne@forem.com>

* Move helper from command to test file

* Update documentation

Co-authored-by: Suzanne Aitchison <suzanne@forem.com>

app/controllers/api/v0/feature_flags_controller.rb

@@ -0,0 +1,27 @@
+module Api
+  module V0
+    # This controller is used for toggling feature flags in the test
+    # environment, specifically for Cypress tests.
+    #
+    # @note: Despite the used methods this controller does not add or remove
+    # the flags themselves, I just wanted distinct methods for enabling and
+    # disabling so we don't need conditional or boolean casting and these were
+    # the most fitting actions.
+    class FeatureFlagsController < ApiController
+      def create
+        FeatureFlag.enable(params[:flag])
+        head :ok
+      end
+
+      def show
+        flag = params[:flag]
+        render json: { flag => FeatureFlag.enabled?(flag) }
+      end
+
+      def destroy
+        FeatureFlag.disable(params[:flag])
+        head :ok
+      end
+    end
+  end
+end

app/lib/rails_env_constraint.rb

@@ -0,0 +1,18 @@
+# Used as routing constraint to expose routes only in certain environments.
+class RailsEnvConstraint
+  # @param [Array<string>] allowed_envs the environments the route(s) will be
+  #   available in.
+  def initialize(allowed_envs:)
+    @allowed_envs = allowed_envs
+  end
+
+  # Returns true if we're in an allowed env
+  #
+  # @note We always ignore the request argument since it's not used.
+  # @return [Boolean]
+  def matches?(_req = nil)
+    # NOTE: ActiveSupport::StringInquirer works with all string methods, so
+    # e.g. "test" == "test".inquiry works as expected.
+    @allowed_envs.any?(Rails.env)
+  end
+end

config/routes.rb

@@ -84,6 +84,10 @@ Rails.application.routes.draw do
           resources :articles, only: [:index], to: "organizations#articles"
         end
         resource :instance, only: %i[show]
+
+        constraints(RailsEnvConstraint.new(allowed_envs: %w[test])) do
+          resource :feature_flags, only: %i[create show destroy], param: :flag
+        end
       end
     end
 

cypress/integration/seededFlows/toggleFeatureFlags.spec.js

@@ -0,0 +1,18 @@
+describe('Toggling feature flags', () => {
+  function checkFeatureFlag(flag, expected) {
+    return cy
+      .request('GET', `/api/feature_flags?flag=${flag}`)
+      .should((response) => {
+        expect(response.body).to.deep.equal({ [flag]: expected });
+      });
+  }
+
+  it('toggles and verifies feature flags', () => {
+    const flag = 'test_feature_flag';
+    checkFeatureFlag(flag, false);
+    cy.enableFeatureFlag(flag);
+    checkFeatureFlag(flag, true);
+    cy.disableFeatureFlag(flag);
+    checkFeatureFlag(flag, false);
+  });
+});

cypress/support/commands.js

@@ -342,3 +342,25 @@ Cypress.Commands.add('createResponseTemplate', ({ title, content }) => {
     `utf8=%E2%9C%93&response_template%5Btitle%5D=${encodedTitle}&response_template%5Bcontent%5D=${encodedContent}`,
   );
 });
+
+/**
+ * Enables a feature flag.
+ *
+ * @param {string} flag The name of the feature flag to enable.
+ *
+ * @returns {Cypress.Chainable<Cypress.Response>} A cypress request for enabling a feature flag.
+ */
+Cypress.Commands.add('enableFeatureFlag', (flag) => {
+  return cy.request('POST', '/api/feature_flags', { flag });
+});
+
+/**
+ * Disables a feature flag.
+ *
+ * @param {string} flag The name of the feature flag to disable.
+ *
+ * @returns {Cypress.Chainable<Cypress.Response>} A cypress request for disabling a feature flag.
+ */
+Cypress.Commands.add('disableFeatureFlag', (flag) => {
+  return cy.request('DELETE', `/api/feature_flags?flag=${flag}`);
+});

spec/lib/rails_env_constraint_spec.rb

@@ -0,0 +1,13 @@
+require "rails_helper"
+
+RSpec.describe RailsEnvConstraint, type: :lib do
+  it "matches only in the correct environments", :aggregate_failures do
+    constraint = described_class.new(allowed_envs: %w[development])
+
+    allow(Rails).to receive(:env).and_return("development")
+    expect(constraint.matches?).to be true
+
+    allow(Rails).to receive(:env).and_return("production")
+    expect(constraint.matches?).to be false
+  end
+end

spec/requests/api/v0/feature_flags_spec.rb

@@ -0,0 +1,64 @@
+require "rails_helper"
+
+RSpec.describe "Api::V0::FeatureFlagsController", type: :request do
+  let(:flag) { "test_flag" }
+  let(:params) { { flag: flag } }
+
+  it "is not available in the production environment" do
+    # We really need an ActiveSupport::StringInquirer here
+    # rubocop:disable Rails/Inquiry
+    allow(Rails).to receive(:env).and_return("production".inquiry)
+    # rubocop:enable Rails/Inquiry
+
+    expect do
+      post api_feature_flags_path, params: params
+    end.to raise_error(ActionController::RoutingError)
+  end
+
+  context "when toggling feature flags" do
+    before { FeatureFlag.add(flag) }
+
+    after { FeatureFlag.remove(flag) }
+
+    it "can enable a disabled feature flag" do
+      FeatureFlag.disable(flag)
+
+      expect do
+        post api_feature_flags_path, params: params
+      end.to change { FeatureFlag.enabled?(flag) }.from(false).to(true)
+    end
+
+    it "keeps the flag enabled when it was already enabled" do
+      FeatureFlag.enable(flag)
+
+      expect do
+        post api_feature_flags_path, params: params
+      end.not_to change { FeatureFlag.enabled?(flag) }.from(true)
+    end
+
+    it "can disable an enabled feature flag" do
+      FeatureFlag.enable(flag)
+
+      expect do
+        delete api_feature_flags_path, params: params
+      end.to change { FeatureFlag.enabled?(flag) }.from(true).to(false)
+    end
+
+    it "keeps the flag disabled when it was already disabled" do
+      FeatureFlag.disable(flag)
+
+      expect do
+        delete api_feature_flags_path, params: params
+      end.not_to change { FeatureFlag.enabled?(flag) }.from(false)
+    end
+
+    it "shows the current value of a feature flag" do
+      FeatureFlag.enable(flag)
+
+      get api_feature_flags_path(flag: flag)
+
+      parsed_response = JSON.parse(response.body)
+      expect(parsed_response[flag]).to be true
+    end
+  end
+end