Make Regexps spouted in error message easier to read.

Becomes:

```
Expected at least 1 element matching "div:match('id', "/wups/")", found 0..
Expected 0 to be >= 1
```

Instead of saying "\"(?-mix:wups)\"".

Author: kaspth

lib/rails/dom/testing/assertions/selector_assertions/html_selector.rb

@@ -7,7 +7,7 @@ class HTMLSelector #:nodoc:
   def initialize(values, previous_selection = nil, &root_fallback)
     @values = values
     @root = extract_root(previous_selection, root_fallback)
-    @css_selector = @selector = extract_selector
+    extract_selectors
     @tests = extract_equality_tests
     @message = @values.shift
 
@@ -73,15 +73,15 @@ def extract_root(previous_selection, root_fallback)
     end
   end
 
-  def extract_selector
+  def extract_selectors
     selector = @values.shift
 
     unless selector.is_a? String
       raise ArgumentError, "Expecting a selector as the first argument"
     end
 
-    context.substitute!(selector, @values)
-    selector
+    @css_selector = context.substitute!(selector, @values.dup, true)
+    @selector     = context.substitute!(selector, @values)
   end
 
   def extract_equality_tests

lib/rails/dom/testing/assertions/selector_assertions/substitution_context.rb

@@ -3,18 +3,26 @@ def initialize
     @substitute = '?'
   end
 
-  def substitute!(selector, values)
+  def substitute!(selector, values, format_for_presentation = false)
+    selector = selector.dup
+
     while !values.empty? && substitutable?(values.first) && selector.index(@substitute)
-      selector.sub! @substitute, matcher_for(values.shift)
+      selector.sub! @substitute, matcher_for(values.shift, format_for_presentation)
     end
+
+    selector
   end
 
   def match(matches, attribute, matcher)
     matches.find_all { |node| node[attribute] =~ Regexp.new(matcher) }
   end
 
   private
-    def matcher_for(value)
+    def matcher_for(value, format_for_presentation)
+      if format_for_presentation && value.is_a?(Regexp)
+        value = value.inspect # Inspect Regexps for readability in error messages.
+      end
+
       value.to_s.inspect # Nokogiri doesn't like arbitrary values without quotes, hence inspect.
     end
 

test/selector_assertions_test.rb

@@ -232,6 +232,16 @@ def test_css_select_with_invalid_selector
     end
   end
 
+  def test_nested_assert_select_with_match_failure_shows_nice_regex
+    render_html %Q{<div id="1">foo</div>}
+
+    error = assert_raises Minitest::Assertion do
+      assert_select "div:match('id', ?)", /wups/
+    end
+
+    assert_match %Q{div:match('id', "/wups/")}, error.message
+  end
+
   def test_feed_item_encoded
     render_xml <<-EOF
 <rss version="2.0">