Writing a new Drupal 8 Module using Test-Driven Development (TDD)
I recently gave a talk on automated testing in Drupal talk at DrupalCamp
Dublin and as a lunch and learn session for my colleagues at Microserve. As
part of the talk, I gave an example of how to build a Drupal 8 module using a
test driven approach. I’ve released the module code on GitHub, and this
post outlines the steps of the process.
Prerequisites
You have created a core/phpunit.xml file based on core/phpunit.xml.dist, and
populated it with your database credentials so that PHPUnit can bootstrap the
Drupal database as part of the tests. Here is an example.
Acceptance Criteria
For the module, we are going to satisfy this example acceptance criteria:
As a site visitor, I want to see all published pages at /pages Ordered
alphabetically by title
Initial Setup
Let’s start by writing the minimal code needed in order for the new module to be
enabled. In Drupal 8, this is the .info.yml file.
# tdd_dublin.info.yml
name: 'TDD Dublin'
excerpt: 'A demo module for DrupalCamp Dublin to show test driven module development.'
core: 8.x
type: module
We can also add the test file structure at this point too. We’ll call it
PageTestTest.php and put it within a tests/src/Functional directory. As this
is a functional test, it extends the BrowserTestBase class, and we need to
ensure that the tdd_dublin module is enabled by adding it to the $modules
array.
// tests/src/Functional/PageListTest.php
namespace Drupal\Tests\tdd_dublin\Functional;
use Drupal\Tests\BrowserTestBase\BrowserTestBase;
class PageListTest extends BrowserTestBase {
protected static $modules = ['tdd_dublin'];
}
With this in place, we can now start adding test methods.
Ensure that the Listing page Exists
Writing the First Test
Let’s start by testing that the listing page exists at /pages. We can do this by
loading the page and checking the status code. If the page exists, the code will
be 200, otherwise it will be 404.
I usually like to write comments first within the test method, just to outline
the steps that I'm going to take and then replace it with code.
public function testListingPageExists() {
// Go to /pages and check that it is accessible by checking the status
// code.
}
We can use the drupalGet() method to browse to the required path, i.e.
/pages, and then write an assertion for the response code value.
public function testListingPageExists() {
$this->drupalGet('pages');
$this->assertSession()->statusCodeEquals(200);
}
Running the Test
In order to run the tests, you either need to include -c core or be inside the
core directory when running the command, to ensure that the test classes are
autoloaded so can be found, though the path to the vendor directory may be
different depending on your project structure. You can also specify a path
within which to run the tests - e.g. within the module’s test directory.
Note: I’m using Docksal, and I’ve noticed that I need to run the tests from within the CLI container. You can do this by running the fin bash command.
1) Drupal\Tests\tdd_dublin\Functional\PageListTest::testListingPageExists
Behat\Mink\Exception\ExpectationException: Current response status code is 404, but 200 expected.
FAILURES!
Tests: 1, Assertions: 1, Errors: 1.
Because the route does not yet exist, the response code returned is 404, so the
test fails.
Now we can make it pass by adding the page. For this, I will use the Views
module, though you could achieve the same result with a custom route and a
Controller.
Building the View
To begin with, I will create a view showing all types of content with a default
sort order of newest first. We will use further tests to ensure that only the
correct content is returned and that it is ordered correctly.
The only addition I will make to the view is to add a path at pages, as per
the acceptance criteria.
Exporting the View
With the first version of the view built, it needs to be incldued within the
module so that it can be enabled when the test is run. To do this, we need to
export the configuration for the view, and place it within the module’s
config/install directory. This can be done using the drush config-export
command or from within the Drupal UI. In either case, the uid line at the top
of the file needs to be removed so the configuration can be installed.
This error is identifying unmet dependencies within the module’s configuration.
In this case, the view that we’ve added depends on the node and views modules,
but these aren’t enabled. To fix this, we can add the extra modules as
dependencies of tdd_dublin so they will be enabled too.
With the modules enabled, we can see one more unmet dependency for
node.type.page. This means that we need a page content type to be able to
install the view. We can fix this in the same way as before, by exporting the
configuration and copying it into the config/install directory.
With this in place, the test should now pass - and it does.
Time: 26.04 seconds, Memory: 6.00MB
OK (1 test, 1 assertion)
We now have a test to ensure that the listing page exists.
Ensure that only Published Pages are Shown
Writing the Test
Now that we have a working page, we can now move on to checking that the correct
content is returned. Again, I’ll start by writing comments and then translate
that into code.
The objectives of this test are:
To ensure that only page nodes are returned.
To ensure that only published nodes are returned.
public function testOnlyPublishedPagesAreShown() {
// Given that a have a mixture of published and unpublished pages, as well
// as other types of content.
// When I view the page.
// Then I should only see the published pages.
}
In order to test the different scenarios, I will create an additional "article"
content type, create a node of this type as well as one published and one
unpublished page. From this combination, I only expect one node to be visible.
public function testOnlyPublishedPagesAreShown() {
$this->drupalCreateContentType(['type' => 'article']);
$this->drupalCreateNode(['type' => 'page', 'status' => TRUE]);
$this->drupalCreateNode(['type' => 'article']);
$this->drupalCreateNode(['type' => 'page', 'status' => FALSE]);
// When I view the page.
// Then I should only see the published pages.
}
We could use drupalGet() again to browse to the page and write assertions
based on the rendered HTML, though I’d rather do this against the data returned
from the view itself. This is so that the test isn’t too tightly coupled to the
presentation logic, and we won’t be in a situation where at a later date the
test fails because of changes made to how the data is displayed.
Rather, I’m going to use views_get_view_result() to programmatically get the
result of the view. This returns an array of Drupal\views\ResultRow objects,
which contain the nodes. I can use array_column to extract the node IDs from
the view result into an array.
public function testOnlyPublishedPagesAreShown() {
$this->drupalCreateContentType(['type' => 'article']);
$this->drupalCreateNode(['type' => 'page', 'status' => TRUE]);
$this->drupalCreateNode(['type' => 'article']);
$this->drupalCreateNode(['type' => 'page', 'status' => FALSE]);
$result = views_get_view_result('pages');
$nids = array_column($result, 'nid');
// Then I should only see the published pages.
}
From the generated nodes, I can use assertEquals() to compare the returned
node IDs from the view against an array of expected node IDs - in this case, I
expect only node 1 to be returned.
The test fails as no extra conditions have been added to the view, though the
default "Content: Published" filter is already excluding one of the page nodes.
We can see from the output from the test that node 1 (a page) and node 2 (the
article) are both being returned.
1) Drupal\Tests\tdd_dublin\Functional\PageListTest::testOnlyPublishedPagesAreShown
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
Array (
- 0 => 1
+ 0 => '2'
+ 1 => '1'
)
FAILURES!
Tests: 1, Assertions: 3, Failures: 1.
Updating the Test
We can fix this by adding another condition to the view, to only show content
based on the node type - i.e. only return page nodes.
Once the view is updated and the configuration is updated within the module, the
test should then pass - and it does.
Time: 24.76 seconds, Memory: 6.00MB
OK (1 test, 3 assertions)
Ensure that the Pages are in the Correct Order
Writing the Test
As we know that the correct content is being returned, we can now focus on
displaying it in the correct order. We’ll start again by adding a new test
method and filling out the comments.
public function testResultsAreOrderedAlphabetically() {
// Given I have multiple nodes with different titles.
// When I view the pages list.
// Then I should see pages in the correct order.
}
To begin with this time, I’ll create a number of different nodes and specify the
title for each. These are intentionally in the incorrect order alphabetically so
that we can see the test fail initially and then see it pass after making a
change so we know that the change worked.
public function testResultsAreOrderedAlphabetically() {
$this->drupalCreateNode(['title' => 'Page A']);
$this->drupalCreateNode(['title' => 'Page D']);
$this->drupalCreateNode(['title' => 'Page C']);
$this->drupalCreateNode(['title' => 'Page B']);
// When I view the pages list.
// Then I should see pages in the correct order.
}
We can use the same method as the previous test to get the returned IDs, using
views_get_view_result() and array_column(), and assert that the returned
node IDs match the expected node IDs in the specified order. Based on the
defined titles, the order should be 1, 4, 3, 2.
As expected the test fails, as the default sort criteria in the view orders the
results by their created date.
In the test output, we can see the returned results are in sequential order so
the results array does not match the expected one.
This would be particularly more complicated to test if I was using drupalGet()
and having to parse the HTML, compared to getting the results as an array from
the view programmatically.
This can be fixed by removing the default sort criteria and adding a new one
based on "Content: Title".
Again, once the view has been updated and exported, the test should pass - and
it does.
Time: 27.55 seconds, Memory: 6.00MB
OK (1 test, 2 assertions)
Ensure all Tests Still Pass
Now we know that all the tests pass individually, all of the module tests should
now be run to ensure that they all still pass and that there have been no
regressions due to any of the changes.
They all pass, so we be confident that the code works as expected, we can
continue to refactor if needed, and if any changes are made to this module at a
later date, we have the tests to ensure that any regressions are caught and
fixed before deployment.
Next Steps
I’ve started looking into whether some of the tests can be rewritten as kernel
tests, which should result in quicker test execution. I will post any updated
code to the GitHub repository, and will also do another blog post
highlighting the differences between functional and kernel tests and the steps
taken to do the conversion.
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About me
I'm an Acquia-certified Drupal Triple Expert with 17 years of experience, an open-source software maintainer and Drupal core contributor, public speaker, live streamer, and host of the Beyond Blocks podcast.