Check-Driving HTML Templates

After a decade or extra the place Single-Web page-Purposes generated by
JavaScript frameworks have
develop into the norm, we see that server-side rendered HTML is changing into
common once more, additionally because of libraries equivalent to HTMX or Turbo. Writing a wealthy net UI in a
historically server-side language like Go or Java is not simply doable,
however a really enticing proposition.

We then face the issue of how one can write automated assessments for the HTML
components of our net functions. Whereas the JavaScript world has advanced highly effective and refined methods to check the UI,
ranging in dimension from unit-level to integration to end-to-end, in different
languages we would not have such a richness of instruments accessible.

When writing an internet software in Go or Java, HTML is usually generated
by way of templates, which include small fragments of logic. It’s definitely
doable to check them not directly by way of end-to-end assessments, however these assessments
are sluggish and costly.

We will as a substitute write unit assessments that use CSS selectors to probe the
presence and proper content material of particular HTML components inside a doc.
Parameterizing these assessments makes it straightforward so as to add new assessments and to obviously
point out what particulars every take a look at is verifying. This strategy works with any
language that has entry to an HTML parsing library that helps CSS
selectors; examples are supplied in Go and Java.

Stage 1: checking for sound HTML

The primary factor we need to test is that the HTML we produce is
mainly sound. I do not imply to test that HTML is legitimate based on the
W3C; it might be cool to do it, however it’s higher to start out with a lot easier and quicker checks.
As an illustration, we would like our assessments to
break if the template generates one thing like

<div>foo</p>

Let’s examine how one can do it in levels: we begin with the next take a look at that
tries to compile the template. In Go we use the usual html/template bundle.

  func Test_wellFormedHtml(t *testing.T) {
    templ := template.Should(template.ParseFiles("index.tmpl"))
    _ = templ
  }

In Java, we use jmustache
as a result of it is quite simple to make use of; Freemarker or
Velocity are different widespread decisions.

Java

  @Check
  void indexIsSoundHtml() {
      var template = Mustache.compiler().compile(
              new InputStreamReader(
                      getClass().getResourceAsStream("/index.tmpl")));
  }

If we run this take a look at, it’s going to fail, as a result of the index.tmpl file does
not exist. So we create it, with the above damaged HTML. Now the take a look at ought to cross.

Then we create a mannequin for the template to make use of. The applying manages a todo-list, and
we will create a minimal mannequin for demonstration functions.

  func Test_wellFormedHtml(t *testing.T) {
    templ := template.Should(template.ParseFiles("index.tmpl"))
    mannequin := todo.NewList()
    _ = templ
    _ = mannequin
  }

Java

  @Check
  void indexIsSoundHtml() {
      var template = Mustache.compiler().compile(
              new InputStreamReader(
                      getClass().getResourceAsStream("/index.tmpl")));
      var mannequin = new TodoList();
  }

Now we render the template, saving the leads to a bytes buffer (Go) or as a String (Java).

  func Test_wellFormedHtml(t *testing.T) {
    templ := template.Should(template.ParseFiles("index.tmpl"))
    mannequin := todo.NewList()
    var buf bytes.Buffer
    err := templ.Execute(&buf, mannequin)
    if err != nil {
      panic(err)
    }
  }

Java

  @Check
  void indexIsSoundHtml() {
      var template = Mustache.compiler().compile(
              new InputStreamReader(
                      getClass().getResourceAsStream("/index.tmpl")));
      var mannequin = new TodoList();
  
      var html = template.execute(mannequin);
  }

At this level, we need to parse the HTML and we count on to see an
error, as a result of in our damaged HTML there’s a div ingredient that
is closed by a p ingredient. There’s an HTML parser within the Go
normal library, however it’s too lenient: if we run it on our damaged HTML, we do not get an
error. Fortunately, the Go normal library additionally has an XML parser that may be
configured to parse HTML (because of this Stack Overflow reply)

  func Test_wellFormedHtml(t *testing.T) {
    templ := template.Should(template.ParseFiles("index.tmpl"))
    mannequin := todo.NewList()
    
    // render the template right into a buffer
    var buf bytes.Buffer
    err := templ.Execute(&buf, mannequin)
    if err != nil {
      panic(err)
    }
  
    // test that the template will be parsed as (lenient) XML
    decoder := xml.NewDecoder(bytes.NewReader(buf.Bytes()))
    decoder.Strict = false
    decoder.AutoClose = xml.HTMLAutoClose
    decoder.Entity = xml.HTMLEntity
    for {
      _, err := decoder.Token()
      change err {
      case io.EOF:
        return // We're performed, it is legitimate!
      case nil:
        // do nothing
      default:
        t.Fatalf("Error parsing html: %s", err)
      }
    }
  }

	characteristic	CSS selector
①	All of the objects	ul.todo-list li
②	Accomplished objects	ul.todo-list li.accomplished
⓷	Gadgets left	span.todo-count
④	Highlighted navigation hyperlink	ul.filters a.chosen
⑤	Clear accomplished button	button.clear-completed

Check-Driving HTML Templates

Stage 1: checking for sound HTML

Stage 2: testing HTML construction

What else ought to we take a look at?

Testing HTML content material

Check each content material and soundness on the identical time

The second take a look at

Make it straightforward so as to add new assessments

Making the desk extra expressive, on the expense of the take a look at code

Stage 3: testing HTML behaviour

Loading the web page within the Playwright browser

Figuring out todo objects

Clicking on a todo merchandise

Spherical-trip to the server

Bonus degree: Stringly asserted

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