Merge pull request #160 from nevir/feature/MultipleExpectations

Add `RSpec/MultipleExpectations` cop

.rubocop.yml

@@ -1,5 +1,7 @@
 require: rubocop-rspec
 
+inherit_from: .rubocop_todo.yml
+
 AllCops:
   DisplayCopNames: true
   TargetRubyVersion: 2.2

.rubocop_todo.yml

@@ -0,0 +1,11 @@
+# This configuration was generated by
+# `rubocop --auto-gen-config`
+# on 2016-08-05 22:48:55 -0700 using RuboCop version 0.42.0.
+# The point is for the user to remove these configuration records
+# one by one as the offenses are removed from the code base.
+# Note that changes in the inspected code, or installation of new
+# versions of RuboCop, may require this file to be generated again.
+
+# Offense count: 8
+RSpec/MultipleExpectations:
+  Max: 3

CHANGELOG.md

@@ -10,6 +10,8 @@
 * Add `NestedGroups` cop for detecting excessive example group nesting. ([@backus][])
 * Add `MaxNesting` configuration option for `NestedGroups` cop. ([@backus][])
 * Add `ExpectActual` cop for detecting literal values within `expect(...)`. ([@backus][])
+* Add `MultipleExpectations` cop for detecting multiple `expect(...)` calls within one example. ([@backus][])
+* Add `Max` configuration option for `MultipleExpectations`. ([@backus][])
 
 ## 1.6.0 (2016-08-03)
 

config/default.yml

@@ -37,6 +37,11 @@ RSpec/MultipleDescribes:
   Description: 'Checks for multiple top level describes.'
   Enabled: true
 
+RSpec/MultipleExpectations:
+  Description: 'Checks for multiple `expect(...)` calls in one example.'
+  Enabled: true
+  Max: 1
+
 RSpec/NestedGroups:
   Description: 'Checks for multiple levels of context nesting.'
   Enabled: true

lib/rubocop-rspec.rb

@@ -22,6 +22,7 @@
 require 'rubocop/cop/rspec/focus'
 require 'rubocop/cop/rspec/instance_variable'
 require 'rubocop/cop/rspec/multiple_describes'
+require 'rubocop/cop/rspec/multiple_expectations'
 require 'rubocop/cop/rspec/named_subject'
 require 'rubocop/cop/rspec/nested_groups'
 require 'rubocop/cop/rspec/not_to_not'

lib/rubocop/cop/rspec/multiple_expectations.rb

@@ -0,0 +1,87 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Checks if examples contain too many `expect` calls
+      #
+      # @see http://betterspecs.org/#single Single expectation test
+      #
+      # This cop is configurable using the `Max` option
+      # and works with `--auto-gen-config`.
+      #
+      # @example
+      #
+      #   # bad
+      #   describe UserCreator do
+      #     it 'builds a user' do
+      #       expect(user.name).to eq("John")
+      #       expect(user.age).to eq(22)
+      #     end
+      #   end
+      #
+      #   # good
+      #   describe UserCreator do
+      #     it 'sets the users name' do
+      #       expect(user.name).to eq("John")
+      #     end
+      #
+      #     it 'sets the users age'
+      #       expect(user.age).to eq(22)
+      #     end
+      #   end
+      #
+      # @example configuration
+      #
+      #   # .rubocop.yml
+      #   RSpec/MultipleExpectations:
+      #     Max: 2
+      #
+      #   # not flagged by rubocop
+      #   describe UserCreator do
+      #     it 'builds a user' do
+      #       expect(user.name).to eq("John")
+      #       expect(user.age).to eq(22)
+      #     end
+      #   end
+      #
+      class MultipleExpectations < Cop
+        include RuboCop::RSpec::Language, ConfigurableMax
+
+        MSG = 'Too many expectations.'.freeze
+
+        def_node_matcher :example?, <<-PATTERN
+          (block (send _ {#{Examples::ALL.to_node_pattern}} ...) ...)
+        PATTERN
+
+        def_node_search :expect, '(send _ :expect ...)'
+
+        def on_block(node)
+          return unless example?(node) && (expectations = expect(node))
+
+          return if expectations.count <= max_expectations
+
+          self.max = expectations.count
+
+          flag_example(node, expectation_count: expectations.count)
+        end
+
+        private
+
+        def flag_example(node, expectation_count:)
+          method, = *node
+
+          add_offense(
+            method,
+            :expression,
+            MSG % { total: expectation_count, max: max_expectations }
+          )
+        end
+
+        def max_expectations
+          Integer(cop_config.fetch(parameter_name, 1))
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/rspec/multiple_expectations_spec.rb

@@ -0,0 +1,84 @@
+# frozen_string_literal: true
+
+describe RuboCop::Cop::RSpec::MultipleExpectations, :config do
+  subject(:cop) { described_class.new(config) }
+
+  context 'without configuration' do
+    let(:cop_config) { Hash.new }
+
+    it 'flags multiple expectations' do
+      expect_violation(<<-RUBY)
+        describe Foo do
+          it 'uses expect twice' do
+          ^^^^^^^^^^^^^^^^^^^^^^ Too many expectations.
+            expect(foo).to eq(bar)
+            expect(baz).to eq(bar)
+          end
+        end
+      RUBY
+    end
+
+    it 'approves of one expectation per example' do
+      expect_no_violations(<<-RUBY)
+        describe Foo do
+          it 'does something neat' do
+            expect(neat).to be(true)
+          end
+
+          it 'does something cool' do
+            expect(cool).to be(true)
+          end
+        end
+      RUBY
+    end
+  end
+
+  context 'with configuration' do
+    let(:cop_config) do
+      { 'Max' => '2' }
+    end
+
+    it 'permits two expectations' do
+      expect_no_violations(<<-RUBY)
+        describe Foo do
+          it 'uses expect twice' do
+            expect(foo).to eq(bar)
+            expect(baz).to eq(bar)
+          end
+        end
+      RUBY
+    end
+
+    it 'flags three expectations' do
+      expect_violation(<<-RUBY)
+        describe Foo do
+          it 'uses expect three times' do
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Too many expectations.
+            expect(foo).to eq(bar)
+            expect(baz).to eq(bar)
+            expect(qux).to eq(bar)
+          end
+        end
+      RUBY
+    end
+  end
+
+  it 'generates a todo based on the worst violation' do
+    inspect_source(cop, <<-RUBY)
+      describe Foo do
+        it 'uses expect twice' do
+          expect(foo).to eq(bar)
+          expect(baz).to eq(bar)
+        end
+
+        it 'uses expect three times' do
+          expect(foo).to eq(bar)
+          expect(baz).to eq(bar)
+          expect(qux).to eq(bar)
+        end
+      end
+    RUBY
+
+    expect(cop.config_to_allow_offenses).to eq('Max' => 3)
+  end
+end