Add assert_in_body/assert_not_in_body (rails#54938)

* Add assert_in_body/assert_not_in_body

As a simple encapsulation of checking a response body for a piece of
text without having to go through a heavy-duty DOM operation.

* Add CHANGELOG entry

* Appease Rubocop

* Escape text so it doesnt trigger regular expressions inadvertedly

Author: dhh

actionpack/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Add assert_in_body/assert_not_in_body as the simplest way to check if a piece of text is in the response body.
+
+    *DHH*
+
 *   Include cookie name when calculating maximum allowed size.
 
     *Hartley McGuire*

actionpack/lib/action_dispatch/testing/assertions/response.rb

@@ -71,6 +71,20 @@ def assert_redirected_to(url_options = {}, options = {}, message = nil)
         assert_operator redirect_expected, :===, redirect_is, message
       end
 
+      # Asserts that the given +text+ is present somewhere in the response body.
+      #
+      #     assert_in_body fixture(:name).description
+      def assert_in_body(text)
+        assert_match(/#{Regexp.escape(text)}/, @response.body)
+      end
+
+      # Asserts that the given +text+ is not present anywhere in the response body.
+      #
+      #     assert_not_in_body fixture(:name).description
+      def assert_not_in_body(text)
+        assert_no_match(/#{Regexp.escape(text)}/, @response.body)
+      end
+
       private
         # Proxy to to_param if the object will respond to it.
         def parameterize(value)

actionpack/test/controller/action_pack_assertions_test.rb

@@ -496,6 +496,12 @@ def test_assert_response_failure_response_with_no_exception
     assert_response 500
     assert_equal "Boom", response.body
   end
+
+  def test_assert_in_body
+    post :raise_exception_on_get
+    assert_in_body "request method: POST"
+    assert_not_in_body "request method: GET"
+  end
 end
 
 class ActionPackHeaderTest < ActionController::TestCase