Take a look at-Driving HTML Templates
After a decade or extra the place Single-Web page-Functions generated by
JavaScript frameworks have
become the norm, we see that server-side rendered HTML is changing into
in style once more, additionally due to libraries corresponding to HTMX or Turbo. Writing a wealthy internet UI in a
historically server-side language like Go or Java is not simply doable,
however a really engaging proposition.
We then face the issue of the way to write automated exams for the HTML
components of our internet functions. Whereas the JavaScript world has advanced powerful and sophisticated methods to check the UI,
ranging in dimension from unit-level to integration to end-to-end, in different
languages we don’t have such a richness of instruments accessible.
When writing an online software in Go or Java, HTML is often generated
by templates, which include small fragments of logic. It’s actually
doable to check them not directly by end-to-end exams, however these exams
are sluggish and costly.
We will as a substitute 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 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 solution to test
{that a} template works is to render it to HTML and open it in a browser,
proper?
There’s some reality on this; unit exams 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, normally the template breaks
in an apparent means, so the error is shortly noticed.
Then again:
- 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 affect the
template? We would get an error at runtime! - Templates usually include logic, corresponding to if-then-else’s or iterations over arrays of things,
and when the array is empty, we frequently want to indicate one thing completely 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 completely different leads to completely different browsers, on completely different units. It is good
to test that the HTML constructions we’re constructing in our templates correspond to
what we predict.
It seems that test-driving HTML templates is straightforward; let’s examine the way to
do it in Go and Java. I might 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 expertise, so long as now we have
entry to an appropriate HTML parser.
This text is a bit lengthy; it’s your decision to check out the
final solution in Go or
in Java,
or jump to the conclusions.
Degree 1: checking for sound HTML
The primary factor we wish to test is that the HTML we produce is
principally sound. I do not imply to test that HTML is legitimate in line with the
W3C; it could be cool to do it, but it surely’s higher to start out with a lot less complicated and quicker checks.
As an example, we wish our exams to
break if the template generates one thing like
<div>foo</p>
Let’s have a look at the way to do it in levels: we begin with the next check that
tries to compile the template. In Go we use the usual html/template
package deal.
Go
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 decisions.
Java
@Take a look at void indexIsSoundHtml() var template = Mustache.compiler().compile( new InputStreamReader( getClass().getResourceAsStream("/index.tmpl")));
If we run this check, it would 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 move.
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.
Go
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).
Go
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
component that
is closed by a p
component. There’s an HTML parser within the Go
customary library, however it’s too lenient: if we run it on our damaged HTML, we do not get an
error. Fortunately, the Go customary library additionally has an XML parser that may be
configured to parse HTML (due to this Stack Overflow answer)
Go
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 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)
This code configures the HTML parser to have the precise stage of leniency
for HTML, after which parses the HTML token by token. Certainly, we see the error
message we needed:
--- FAIL: Test_wellFormedHtml (0.00s) index_template_test.go:61: Error parsing html: XML syntax error on line 4: surprising finish component </p>
In Java, a flexible library to make use of is jsoup:
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);
var parser = Parser.htmlParser().setTrackErrors(10);
Jsoup.parse(html, "", parser);
assertThat(parser.getErrors()).isEmpty();
And we see it fail:
java.lang.AssertionError: Anticipating empty however was:<[<1:13>: Unexpected EndTag token [</p>] when in state [InBody],
Success! Now if we copy over the contents of the TodoMVC
template to our index.tmpl
file, the check passes.
The check, nonetheless, is just too verbose: we extract two helper features, in
order to make the intention of the check clearer, and we get
Go
func Test_wellFormedHtml(t *testing.T) mannequin := todo.NewList() buf := renderTemplate("index.tmpl", mannequin) assertWellFormedHtml(t, buf)
Java
@Take a look at void indexIsSoundHtml() var mannequin = new TodoList(); var html = renderTemplate("/index.tmpl", mannequin); assertSoundHtml(html);
Degree 2: testing HTML construction
What else ought to we check?
We all know that the appears of a web page can solely be examined, finally, by a
human how it’s rendered in a browser. Nevertheless, there may be usually
logic in templates, and we wish to have the ability to check that logic.
One is likely to be tempted to check the rendered HTML with string equality,
however this method fails in follow, as a result of templates include a variety of
particulars that make string equality assertions impractical. The assertions
develop into very verbose, and when studying the assertion, it turns into troublesome
to grasp what it’s that we’re making an attempt to show.
What we’d like
is a way to say that some components of the rendered HTML
correspond to what we count on, and to ignore all the small print we do not
care about. A technique to do that is by operating queries with the CSS selector language:
it’s a highly effective language that enables us to pick the
components that we care about from the entire HTML doc. As soon as now we have
chosen these components, we (1) depend that the variety of component returned
is what we count on, and (2) that they include the textual content or different content material
that we count on.
The UI that we’re speculated to generate appears like this:
There are a number of particulars which might be rendered dynamically:
- The variety of objects and their textual content content material change, clearly
- The model of the todo-item adjustments when it is accomplished (e.g., the
second) - The “2 objects left” textual content will change with the variety of non-completed
objects - One of many three buttons “All”, “Lively”, “Accomplished” might be
highlighted, relying on the present url; for example if we determine that the
url that reveals solely the “Lively” objects is/lively
, then when the present url
is/lively
, the “Lively” button must be surrounded by a skinny purple
rectangle - The “Clear accomplished” button ought to solely be seen if any merchandise is
accomplished
Every of this issues could be examined with the assistance of CSS selectors.
It is a snippet from the TodoMVC template (barely simplified). I
haven’t but added the dynamic bits, so what we see right here is static
content material, supplied for example:
index.tmpl
<part class="todoapp"> <ul class="todo-list"> <!-- These are right here simply to indicate the construction of the record objects --> <!-- Record objects ought to get the category `accomplished` when marked as accomplished --> <li class="accomplished"> ② <div class="view"> <enter class="toggle" kind="checkbox" checked> <label>Style JavaScript</label> ① <button class="destroy"></button> </div> </li> <li> <div class="view"> <enter class="toggle" kind="checkbox"> <label>Purchase a unicorn</label> ① <button class="destroy"></button> </div> </li> </ul> <footer class="footer"> <!-- This must be `0 objects left` by default --> <span class="todo-count"><sturdy>0</sturdy> merchandise left</span> ⓷ <ul class="filters"> <li> <a class="chosen" href="#/">All</a> ④ </li> <li> <a href="#/lively">Lively</a> </li> <li> <a href="#/accomplished">Accomplished</a> </li> </ul> <!-- Hidden if no accomplished objects are left ↓ --> <button class="clear-completed">Clear accomplished</button> ⑤ </footer> </part>
By wanting on the static model of the template, we will deduce which
CSS selectors can be utilized to determine the related components for the 5 dynamic
options listed above:
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 |
We will use these selectors to focus our exams on simply the issues we wish to check.
Testing HTML content material
The primary check will search for all of the objects, and show that the information
arrange by the check is rendered appropriately.
func Test_todoItemsAreShown(t *testing.T) mannequin := todo.NewList() mannequin.Add("Foo") mannequin.Add("Bar") buf := renderTemplate(mannequin) // assert there are two <li> components contained in the <ul class="todo-list"> // assert the primary <li> textual content is "Foo" // assert the second <li> textual content is "Bar"
We want a solution to question the HTML doc with our CSS selector; a very good
library for Go is goquery, that implements an API impressed by jQuery.
In Java, we hold utilizing the identical library we used to check for sound HTML, specifically
jsoup. Our check turns into:
Go
func Test_todoItemsAreShown(t *testing.T) mannequin := todo.NewList() mannequin.Add("Foo") mannequin.Add("Bar") buf := renderTemplate("index.tmpl", mannequin) // parse the HTML with goquery doc, err := goquery.NewDocumentFromReader(bytes.NewReader(buf.Bytes())) if err != nil // if parsing fails, we cease the check right here with t.FatalF t.Fatalf("Error rendering template %s", err) // assert there are two <li> components contained in the <ul class="todo-list"> choice := doc.Discover("ul.todo-list li") assert.Equal(t, 2, choice.Size()) // assert the primary <li> textual content is "Foo" assert.Equal(t, "Foo", textual content(choice.Nodes[0])) // assert the second <li> textual content is "Bar" assert.Equal(t, "Bar", textual content(choice.Nodes[1])) func textual content(node *html.Node) string // Just a little mess attributable to the truth that goquery has // a .Textual content() technique on Choice however not on html.Node sel := goquery.SelectionNodes: []*html.Nodenode return strings.TrimSpace(sel.Textual content())
Java
@Take a look at void todoItemsAreShown() throws IOException var mannequin = new TodoList(); mannequin.add("Foo"); mannequin.add("Bar"); var html = renderTemplate("/index.tmpl", mannequin); // parse the HTML with jsoup Doc doc = Jsoup.parse(html, ""); // assert there are two <li> components contained in the <ul class="todo-list"> var choice = doc.choose("ul.todo-list li"); assertThat(choice).hasSize(2); // assert the primary <li> textual content is "Foo" assertThat(choice.get(0).textual content()).isEqualTo("Foo"); // assert the second <li> textual content is "Bar" assertThat(choice.get(1).textual content()).isEqualTo("Bar");
If we nonetheless have not modified the template to populate the record from the
mannequin, this check will fail, as a result of the static template
todo objects have completely different textual content:
Go
--- FAIL: Test_todoItemsAreShown (0.00s) index_template_test.go:44: First record merchandise: need Foo, received Style JavaScript index_template_test.go:49: Second record merchandise: need Bar, received Purchase a unicorn
Java
IndexTemplateTest > todoItemsAreShown() FAILED org.opentest4j.AssertionFailedError: Anticipating: <"Style JavaScript"> to be equal to: <"Foo"> however was not.
We repair it by making the template use the mannequin information:
Go
<ul class="todo-list"> vary .Gadgets <li> <div class="view"> <enter class="toggle" kind="checkbox"> <label> .Title </label> <button class="destroy"></button> </div> </li> finish </ul>
Java – jmustache
<ul class="todo-list"> #allItems <li> <div class="view"> <enter class="toggle" kind="checkbox"> <label> title </label> <button class="destroy"></button> </div> </li> /allItems </ul>
Take a look at each content material and soundness on the identical time
Our check works, however it’s a bit verbose, particularly the Go model. If we’ll have extra
exams, they may develop into repetitive and troublesome to learn, so we make it extra concise by extracting a helper operate for parsing the html. We additionally take away the
feedback, because the code must be clear sufficient
Go
func Test_todoItemsAreShown(t *testing.T) mannequin := todo.NewList() mannequin.Add("Foo") mannequin.Add("Bar") buf := renderTemplate("index.tmpl", mannequin) doc := parseHtml(t, buf) choice := doc.Discover("ul.todo-list li") assert.Equal(t, 2, choice.Size()) assert.Equal(t, "Foo", textual content(choice.Nodes[0])) assert.Equal(t, "Bar", textual content(choice.Nodes[1])) func parseHtml(t *testing.T, buf bytes.Buffer) *goquery.Doc doc, err := goquery.NewDocumentFromReader(bytes.NewReader(buf.Bytes())) if err != nil // if parsing fails, we cease the check right here with t.FatalF t.Fatalf("Error rendering template %s", err) return doc
Java
@Take a look at void todoItemsAreShown() throws IOException var mannequin = new TodoList(); mannequin.add("Foo"); mannequin.add("Bar"); var html = renderTemplate("/index.tmpl", mannequin); var doc = parseHtml(html); var choice = doc.choose("ul.todo-list li"); assertThat(choice).hasSize(2); assertThat(choice.get(0).textual content()).isEqualTo("Foo"); assertThat(choice.get(1).textual content()).isEqualTo("Bar"); non-public static Doc parseHtml(String html) return Jsoup.parse(html, "");
Significantly better! Not less than in my view. Now that we extracted the parseHtml
helper, it is
a good suggestion to test for sound HTML within the helper:
Go
func parseHtml(t *testing.T, buf bytes.Buffer) *goquery.Doc
assertWellFormedHtml(t, buf)
doc, err := goquery.NewDocumentFromReader(bytes.NewReader(buf.Bytes()))
if err != nil
// if parsing fails, we cease the check right here with t.FatalF
t.Fatalf("Error rendering template %s", err)
return doc
Java
non-public static Doc parseHtml(String html) var parser = Parser.htmlParser().setTrackErrors(10); var doc = Jsoup.parse(html, "", parser); assertThat(parser.getErrors()).isEmpty(); return doc;
And with this, we will eliminate the primary check that we wrote, as we are actually testing for sound HTML on a regular basis.
The second check
Now we’re in a very good place for testing extra rendering logic. The
second dynamic characteristic in our record is “Record objects ought to get the category
accomplished
when marked as accomplished”. We will write a check for this:
Go
func Test_completedItemsGetCompletedClass(t *testing.T) mannequin := todo.NewList() mannequin.Add("Foo") mannequin.AddCompleted("Bar") buf := renderTemplate("index.tmpl", mannequin) doc := parseHtml(t, buf) choice := doc.Discover("ul.todo-list li.accomplished") assert.Equal(t, 1, choice.Measurement()) assert.Equal(t, "Bar", textual content(choice.Nodes[0]))
Java
@Take a look at void completedItemsGetCompletedClass() var mannequin = new TodoList(); mannequin.add("Foo"); mannequin.addCompleted("Bar"); var html = renderTemplate("/index.tmpl", mannequin); Doc doc = Jsoup.parse(html, ""); var choice = doc.choose("ul.todo-list li.accomplished"); assertThat(choice).hasSize(1); assertThat(choice.textual content()).isEqualTo("Bar");
And this check could be made inexperienced by including this little bit of logic to the
template:
Go
<ul class="todo-list">
vary .Gadgets
<li class=" if .IsCompleted accomplished finish ">
<div class="view">
<enter class="toggle" kind="checkbox">
<label> .Title </label>
<button class="destroy"></button>
</div>
</li>
finish
</ul>
Java – jmustache
<ul class="todo-list">
#allItems
<li class=" #isCompleted accomplished /isCompleted ">
<div class="view">
<enter class="toggle" kind="checkbox">
<label> title </label>
<button class="destroy"></button>
</div>
</li>
/allItems
</ul>
So little by little, we will check and add the varied dynamic options
that our template ought to have.