Take a look at-Driving HTML Templates

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

We then face the issue of the way to write automated assessments for the HTML
elements of our net purposes. Whereas the JavaScript world has developed highly effective and refined methods to check the UI,
ranging in measurement from unit-level to integration to end-to-end, in different
languages we don’t have such a richness of instruments out there.

When writing an internet software in Go or Java, HTML is often generated
via templates, which comprise small fragments of logic. It’s actually
attainable to check them not directly via end-to-end assessments, however these assessments
are gradual and costly.

We are able to as an alternative write unit assessments that use CSS selectors to probe the
presence and proper content material of particular HTML parts inside a doc.
Parameterizing these assessments makes it simple 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.

Motivation

Why test-drive HTML templates? In spite of everything, essentially the most dependable option to verify
{that a} template works is to render it to HTML and open it in a browser,
proper?

There’s some fact on this; unit assessments can not show {that a} template
works as anticipated when rendered in a browser, so checking them manually
is important. And if we make a
mistake within the logic of a template, often the template breaks
in an apparent manner, so the error is rapidly noticed.

Alternatively:

Counting on guide assessments solely is dangerous; what if we make a change that breaks
a template, and we do not take a look at it as a result of we didn’t assume it will influence the
template? We would get an error at runtime!
Templates typically comprise logic, resembling if-then-else’s or iterations over arrays of things,
and when the array is empty, we frequently want to indicate one thing totally different.
Handbook checking all circumstances, for all of those bits of logic, turns into unsustainable in a short time
There are errors that aren’t seen within the browser. Browsers are extraordinarily
tolerant of inconsistencies in HTML, counting on heuristics to repair our damaged
HTML, however then we would get totally different leads to totally different browsers, on totally different units. It is good
to verify that the HTML buildings we’re constructing in our templates correspond to
what we predict.

It seems that test-driving HTML templates is simple; let’s have a look at the way to
do it in Go and Java. I will likely be utilizing as a place to begin the TodoMVC
template, which is a pattern software used to showcase JavaScript
frameworks.

We are going to see methods that may be utilized to any programming language and templating know-how, so long as we’ve got
entry to an appropriate HTML parser.

This text is a bit lengthy; it’s your decision to try the
closing resolution in Go or
in Java,
or bounce to the conclusions.

Degree 1: checking for sound HTML

The primary factor we wish to verify is that the HTML we produce is
mainly sound. I do not imply to verify that HTML is legitimate in line with the
W3C; it will be cool to do it, nevertheless it’s higher to begin with a lot easier and sooner checks.
As an illustration, we would like our assessments to
break if the template generates one thing like

<div>foo</p>

Let’s have a look at the way to do it in phases: we begin with the next take a look at that
tries to compile the template. In Go we use the usual html/template package deal.

  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

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

If we run this take a look at, it’ll 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 move.

Then we create a mannequin for the template to make use of. The appliance 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

  @Take a look at
  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

  @Take a look at
  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 wish to parse the HTML and we count on to see an
error, as a result of in our damaged HTML there’s a div aspect that
is closed by a p aspect. 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)
    }
  
    // verify that the template could 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()
      swap err {
      case io.EOF:
        return // We're carried out, it is legitimate!
      case nil:
        // do nothing
      default:
        t.Fatalf("Error parsing html: %s", err)
      }
    }
  }

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

Motivation

Degree 1: checking for sound HTML

Degree 2: testing HTML construction

What else ought to we take a look at?

Testing HTML content material

Take a look at each content material and soundness on the identical time

The second take a look at

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