Take a look at-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 turning into
standard once more, additionally due to libraries comparable to HTMX or Turbo. Writing a wealthy internet UI in a
historically server-side language like Go or Java is no longer simply doable,
however a really enticing proposition.

We then face the issue of tips on how to write automated exams for the HTML
components of our internet functions. Whereas the JavaScript world has developed highly effective and subtle methods to check the UI,
ranging in dimension from unit-level to integration to end-to-end, in different
languages we do not need such a richness of instruments accessible.

When writing an online utility in Go or Java, HTML is often generated
via templates, which include small fragments of logic. It’s actually
doable to check them not directly via end-to-end exams, however these exams
are gradual and costly.

We will as an alternative write unit exams that use CSS selectors to probe the
presence and proper content material of particular HTML components inside a doc.
Parameterizing these exams makes it simple so as to add new exams and to obviously
point out what particulars every check is verifying. This method 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 any case, 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 exams can’t 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, normally the template breaks
in an apparent means, so the error is rapidly noticed.

However:

Counting on handbook exams solely is dangerous; what if we make a change that breaks
a template, and we do not check it as a result of we didn’t suppose it could impression the
template? We might get an error at runtime!
Templates typically include logic, comparable to if-then-else’s or iterations over arrays of things,
and when the array is empty, we regularly want to indicate one thing totally different.
Guide 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’d get totally different ends in totally different browsers, on totally different gadgets. It is good
to verify that the HTML constructions we’re constructing in our templates correspond to
what we expect.

It seems that test-driving HTML templates is straightforward; let’s have a look at tips on how to
do it in Go and Java. I can be utilizing as a place to begin the TodoMVC
template, which is a pattern utility used to showcase JavaScript
frameworks.

We are going to see methods that may be utilized to any programming language and templating expertise, so long as now we have
entry to an appropriate HTML parser.

This text is a bit lengthy; you might have considered trying to check out the
last answer in Go or
in Java,
or bounce to the conclusions.

Stage 1: checking for sound HTML

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

<div>foo</p>

Let’s examine tips on how to do it in phases: we begin with the next check 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 frequent selections.

Java

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

If we run this check, it is 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 check ought to go.

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

  @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 ends in 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 need to parse the HTML and we anticipate 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 may be 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 (due to 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()
      change err {
      case io.EOF:
        return // We're completed, it is legitimate!
      case nil:
        // do nothing
      default:
        t.Fatalf("Error parsing html: %s", err)
      }
    }
  }

	function	CSS selector
①	All of the objects	ul.todo-list li
②	Accomplished objects	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

Take a look at-Driving HTML Templates

Motivation

Stage 1: checking for sound HTML

Stage 2: testing HTML construction

What else ought to we check?

Testing HTML content material

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

The second check

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