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---
title: Writing a new Drupal 8 Module using Test Driven Development (TDD)
date: 2017-11-07
tags: [drupal, testing, tdd, simpletest, phpunit]
excerpt:
How to write automated tests and follow test driven development for Drupal
modules.
meta:
image:
url: /images/talks/test-driven-drupal-development.png
width: 2560
height: 1440
type: image/png
promoted: true
---
<p class="text-center" markdown="1">![](/images/blog/drupalcamp-dublin.jpg)</p>
I recently gave a [talk on automated testing in Drupal][0] talk at [DrupalCamp
Dublin][1] 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][2], 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][5].
## Acceptance Criteria
For the module, we are going to satisfy this example acceptance criteria:
> As a site visitor,<br> I want to see all published pages at /pages<br> 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.
```language-yaml
# 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.
```language-php
// 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.
```language-php
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.
```language-php
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.
```language-plain
$ vendor/bin/phpunit -c core modules/custom/tdd_dublin/tests
```
<div class="note" markdown="1">
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.
</div>
```language-plain
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.
![](/images/blog/tdd-drupal-1.png) { .with-border }
The only addition I will make to the view is to add a path at `pages`, as per
the acceptance criteria.
![](/images/blog/tdd-drupal-2.png) { .with-border }
### 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.
Here is the exported view configuration:
```language-yaml
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.
```language-plain
1) Drupal\Tests\tdd_dublin\Functional\PageListTest::testListingPageExists
Drupal\Core\Config\UnmetDependenciesException: Configuration objects provided by <em class="placeholder">tdd_dublin</em> have unmet dependencies: <em class="placeholder">node.type.page (node), views.view.pages (node, views)</em>
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.
```language-yaml
# tdd_dublin.info.yml
dependencies:
- drupal:node
- drupal:views
```
```language-plain
1) Drupal\Tests\tdd_dublin\Functional\PageListTest::testListingPageExists
Drupal\Core\Config\UnmetDependenciesException: Configuration objects provided by <em class="placeholder">tdd_dublin</em> have unmet dependencies: <em class="placeholder">views.view.pages (node.type.page)</em>
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.
```language-plain
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.
```language-php
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.
```language-php
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.
```language-php
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.
```language-php
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.
```language-plain
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.
![](/images/blog/tdd-drupal-3.png) { .with-border }
Once the view is updated and the configuration is updated within the module, the
test should then pass - and it does.
```language-plain
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.
```language-php
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.
```language-php
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.
```language-php
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], $nids);
}
```
### Running the Test
As expected the test fails, as the default sort criteria in the view orders the
results by their created date.
In the test output, we can see the returned results are in sequential order so
the results array does not match the expected one.
This would be particularly more complicated to test if I was using `drupalGet()`
and having to parse the HTML, compared to getting the results as an array from
the view programmatically.
```language-plain
1) Drupal\Tests\tdd_dublin\Functional\PageListTest::testResultsAreOrderedAlphabetically
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
Array (
- 0 => 1
- 1 => 4
- 2 => 3
- 3 => 2
+ 0 => '1'
+ 1 => '2'
+ 2 => '3'
+ 3 => '4'
)
FAILURES!
Tests: 1, Assertions: 2, Failures: 1.
```
### Updating the Test
This can be fixed by removing the default sort criteria and adding a new one
based on "Content: Title".
![](/images/blog/tdd-drupal-4.png) { .with-border }
Again, once the view has been updated and exported, the test should pass - and
it does.
```language-plain
Time: 27.55 seconds, Memory: 6.00MB
OK (1 test, 2 assertions)
```
## Ensure all Tests Still Pass
Now we know that all the tests pass individually, all of the module tests should
now be run to ensure that they all still pass and that there have been no
regressions due to any of the changes.
```language-plain
docker@cli:/var/www$ 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][3], and will also do another blog post
highlighting the differences between functional and kernel tests and the steps
taken to do the conversion.
[0]: {{site.url}}/talks/tdd-test-driven-drupal
[1]: http://2017.drupal.ie
[2]: https://github.com/opdavies/tdd_dublin
[3]: https://packagist.org/packages/tightenco/collect
[4]: http://php.net/manual/en/function.array-column.php
[5]: https://gist.github.com/opdavies/dc5f0cea46ccd349b34a9f3a463c14bb
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