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.

$ vendor/bin/phpunit -c core modules/custom/tdd_dublin/tests

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 included 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.

Here is the exported view configuration:

langcode: en
status: true
dependencies:
module:
- node
- user
id: pages
label: pages
module: views
excerpt: ""
tag: ""
base_table: node_field_data
base_field: nid
core: 8.x
display:
default:
display_plugin: default
id: default
display_title: Master
position: 0
display_options:
access:
type: perm
options:
perm: 'access content'
cache:
type: tag
options: { }
query:
type: views_query
options:
disable_sql_rewrite: false
distinct: false
replica: false
query_comment: ''
query_tags: { }
exposed_form:
type: basic
options:
submit_button: Apply
reset_button: false
reset_button_label: Reset
exposed_sorts_label: 'Sort by'
expose_sort_order: true
sort_asc_label: Asc
sort_desc_label: Desc
pager:
type: mini
options:
items_per_page: 10
offset: 0
id: 0
total_pages: null
expose:
items_per_page: false
items_per_page_label: 'Items per page'
items_per_page_options: '5, 10, 25, 50'
items_per_page_options_all: false
items_per_page_options_all_label: '- All -'
offset: false
offset_label: Offset
tags:
previous: ‹‹
next: ››
style:
type: default
options:
grouping: { }
row_class: ''
default_row_class: true
uses_fields: false
row:
type: fields
options:
inline: { }
separator: ''
hide_empty: false
default_field_elements: true
fields:
title:
id: title
table: node_field_data
field: title
entity_type: node
entity_field: title
label: ''
alter:
alter_text: false
make_link: false
absolute: false
trim: false
word_boundary: false
ellipsis: false
strip_tags: false
html: false
hide_empty: false
empty_zero: false
settings:
link_to_entity: true
plugin_id: field
relationship: none
group_type: group
admin_label: ''
exclude: false
element_type: ''
element_class: ''
element_label_type: ''
element_label_class: ''
element_label_colon: true
element_wrapper_type: ''
element_wrapper_class: ''
element_default_classes: true
empty: ''
hide_alter_empty: true
click_sort_column: value
type: string
group_column: value
group_columns: { }
group_rows: true
delta_limit: 0
delta_offset: 0
delta_reversed: false
delta_first_last: false
multi_type: separator
separator: ', '
field_api_classes: false
filters:
status:
value: '1'
table: node_field_data
field: status
plugin_id: boolean
entity_type: node
entity_field: status
id: status
expose:
operator: ''
group: 1
sorts:
created:
id: created
table: node_field_data
field: created
order: DESC
entity_type: node
entity_field: created
plugin_id: date
relationship: none
group_type: group
admin_label: ''
exposed: false
expose:
label: ''
granularity: second
header: { }
footer: { }
empty: { }
relationships: { }
arguments: { }
display_extenders: { }
cache_metadata:
max-age: -1
contexts:
- 'languages:language_content'
- 'languages:language_interface'
- url.query_args
- 'user.node_grants:view'
- user.permissions
tags: { }
page_1:
display_plugin: page
id: page_1
display_title: Page
position: 1
display_options:
display_extenders: { }
path: pages
cache_metadata:
max-age: -1
contexts:
- 'languages:language_content'
- 'languages:language_interface'
- url.query_args
- 'user.node_grants:view'
- user.permissions
tags: { }

When the test is run again, we see a different error that leads us to the next step.

1) Drupal\Tests\tdd_dublin\Functional\PageListTest::testListingPageExists
Drupal\Core\Config\UnmetDependenciesException: Configuration objects provided by tdd_dublin have unmet dependencies: node.type.page (node), views.view.pages (node, views)

FAILURES!
Tests: 1, Assertions: 0, Errors: 1.

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.

# tdd_dublin.info.yml

dependencies:
- drupal:node
- drupal:views

1) Drupal\Tests\tdd_dublin\Functional\PageListTest::testListingPageExists
Drupal\Core\Config\UnmetDependenciesException: Configuration objects provided by tdd_dublin have unmet dependencies: views.view.pages (node.type.page)

FAILURES!
Tests: 1, Assertions: 0, Errors: 1.

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.

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');

$this->assertEquals([1], $nids);
}

Running the Test

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.

public function testResultsAreOrderedAlphabetically() {
$this->drupalCreateNode(['title' => 'Page A']);
$this->drupalCreateNode(['title' => 'Page D']);
$this->drupalCreateNode(['title' => 'Page C']);
$this->drupalCreateNode(['title' => 'Page B']);

$nids = array_column(views_get_view_result('pages'), 'nid');

$this->assertEquals([1, 4, 3, 2], $nids);
}

Running the Test

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.

1) Drupal\Tests\tdd_dublin\Functional\PageListTest::testResultsAreOrderedAlphabetically
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
Array (
- 0 => 1
- 1 => 4
- 2 => 3
- 3 => 2
+ 0 => '1'
+ 1 => '2'
+ 2 => '3'
+ 3 => '4'
)

FAILURES!
Tests: 1, Assertions: 2, Failures: 1.

Updating the Test

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.

docker@cli:/var/www$ vendor/bin/phpunit -c core modules/custom/tdd_dublin/tests

Testing modules/custom/tdd_dublin/tests
...

Time: 1.27 minutes, Memory: 6.00MB

OK (3 tests, 6 assertions)

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.