Parse ActionView::TestCase#rendered as DocumentFragment
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To integrate with [rails-dom-testing][] and its selector assertions,
`ActionView::TestCase` [defines a `#document_root_element`
method][document_root_element] that parses the HTML into a fully valid
HTML document and returns the "root".
In the case of most Action View partials rendered with `render partial:
"..."`, the resulting document would be invalid, so its constituent
parts (its `<html>`, `<head>`, and `<body>` elements) are synthesized in
during the parsing process. This results in a document whose _contents_
are equivalent to the original HTML string, but whose structure is not.
To share a concrete example:
```ruby
irb(main):002:0> rendered = "<h1>Hello world</h1><h2>Goodbye world</h2>"
=> "<h1>Hello world</h1><h2>Goodbye world</h2>"
irb(main):003:0> root = Rails::Dom::Testing.html_document.parse(rendered).root
=>
#(Element:0x57080 {
...
irb(main):004:0> rendered.to_s
=> "<h1>Hello world</h1><h2>Goodbye world</h2>"
irb(main):005:0> root.to_s
=> "<html><head></head><body><h1>Hello world</h1><h2>Goodbye world</h2></body></html>"
irb(main):006:0> rendered.to_s == root.to_s
=> false
```
Prior to this commit, the parsed HTML content returned from calling
`rendered.html` relied on the same mechanisms as
`#document_root_element`, and parsed the HTML fragment into a full
document, with a synthesized `<html>` element as its root. The
`rendered.html` value should reflect the content that was **rendered**
by the partial, and should not behave the same as
`#document_root_element`.
When the parsing class is changed from [Nokogiri::XML::Document][] to
[Nokogiri::XML::DocumentFragment][], the returned value reflects the
same **exact** content as what was rendered.
To elaborate on the previous example:
```ruby
irb(main):007:0> fragment = Rails::Dom::Testing.html_document_fragment.parse(rendered)
=>
#(DocumentFragment:0x62ee4 {
...
irb(main):008:0> fragment.to_s
=> "<h1>Hello world</h1><h2>Goodbye world</h2>"
irb(main):009:0> rendered.to_s == fragment.to_s
=> true
```
This commit changes the default `rendered.html` behavior to rely on
`Nokogiri::XML::DocumentFragment` instead of `Nokogiri::XML::Document`.
[Nokogiri::XML::Document]: https://nokogiri.org/rdoc/Nokogiri/XML/Document.html
[Nokogiri::XML::DocumentFragment]: https://nokogiri.org/rdoc/Nokogiri/XML/DocumentFragment.html
[document_root_element]: https://github.com/rails/rails-dom-testing/blob/v2.2.0/lib/rails/dom/testing/assertions/selector_assertions.rb#L75
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Motivation / Background
To integrate with rails-dom-testing and its selector assertions,
ActionView::TestCasedefines a#document_root_elementmethod that parses the HTML into a fully valid HTML document and returns the "root".In the case of most Action View partials rendered with
render partial: "...", the resulting document would be invalid, so its constituent parts (its<html>,<head>, and<body>elements) are synthesized during the parsing process. This results in a document whose contents are equivalent to the original HTML string, but whose structure is not.To share a concrete example:
Prior to this commit, the parsed HTML content returned from calling
rendered.htmlrelied on the same mechanisms as#document_root_element, and parsed the HTML fragment into a full document, with a synthesized<html>element as its root. Therendered.htmlvalue should reflect the content that was rendered by the partial, and should not behave the same as#document_root_element.When the parsing class is changed from Nokogiri::XML::Document to Nokogiri::XML::DocumentFragment, the returned value reflects the same exact content as what was rendered.
To elaborate on the previous example:
Detail
This commit changes the default
rendered.htmlbehavior to rely onNokogiri::XML::DocumentFragmentinstead ofNokogiri::XML::Document.Checklist
Before submitting the PR make sure the following are checked:
[Fix #issue-number]