Backport Rails 5 test assertions

#799

test/support/rails5_assetions.rb

@@ -0,0 +1,94 @@
+module ActiveSupport
+  module Testing
+    module Assertions
+      UNTRACKED = Object.new # :nodoc:
+
+      # Assertion that the result of evaluating an expression is changed before
+      # and after invoking the passed in block.
+      #
+      #   assert_changes 'Status.all_good?' do
+      #     post :create, params: { status: { ok: false } }
+      #   end
+      #
+      # You can pass the block as a string to be evaluated in the context of
+      # the block. A lambda can be passed for the block as well.
+      #
+      #   assert_changes -> { Status.all_good? } do
+      #     post :create, params: { status: { ok: false } }
+      #   end
+      #
+      # The assertion is useful to test side effects. The passed block can be
+      # anything that can be converted to string with #to_s.
+      #
+      #   assert_changes :@object do
+      #     @object = 42
+      #   end
+      #
+      # The keyword arguments :from and :to can be given to specify the
+      # expected initial value and the expected value after the block was
+      # executed.
+      #
+      #   assert_changes :@object, from: nil, to: :foo do
+      #     @object = :foo
+      #   end
+      #
+      # An error message can be specified.
+      #
+      #   assert_changes -> { Status.all_good? }, 'Expected the status to be bad' do
+      #     post :create, params: { status: { incident: true } }
+      #   end
+      def assert_changes(expression, message = nil, from: UNTRACKED, to: UNTRACKED, &block)
+        exp = expression.respond_to?(:call) ? expression : -> { eval(expression.to_s, block.binding) }
+
+        before = exp.call
+        retval = yield
+
+        unless from == UNTRACKED
+          error = "#{expression.inspect} isn't #{from.inspect}"
+          error = "#{message}.\n#{error}" if message
+          assert from === before, error
+        end
+
+        after = exp.call
+
+        if to == UNTRACKED
+          error = "#{expression.inspect} didn't changed"
+          error = "#{message}.\n#{error}" if message
+          assert_not_equal before, after, error
+        else
+          error = "#{expression.inspect} didn't change to #{to}"
+          error = "#{message}.\n#{error}" if message
+          assert to === after, error
+        end
+
+        retval
+      end
+
+      # Assertion that the result of evaluating an expression is changed before
+      # and after invoking the passed in block.
+      #
+      #   assert_no_changes 'Status.all_good?' do
+      #     post :create, params: { status: { ok: true } }
+      #   end
+      #
+      # An error message can be specified.
+      #
+      #   assert_no_changes -> { Status.all_good? }, 'Expected the status to be good' do
+      #     post :create, params: { status: { ok: false } }
+      #   end
+      def assert_no_changes(expression, message = nil, &block)
+        exp = expression.respond_to?(:call) ? expression : -> { eval(expression.to_s, block.binding) }
+
+        before = exp.call
+        retval = yield
+        after = exp.call
+
+        error = "#{expression.inspect} did change to #{after}"
+        error = "#{message}.\n#{error}" if message
+        assert_equal before, after, error
+
+        retval
+      end
+    end
+  end
+end

test/test_helper.rb

@@ -11,6 +11,7 @@ require 'minitest/mock'
 require 'capybara/rails'
 require 'capybara/minitest'
 require 'webmock/minitest'
+require 'support/rails5_assetions' # Remove once upgraded to Rails 5
 
 Setting.address_processing = false