Multi-module Lint Rules: Tests 🧪

In my previous post, I talked about how to write a Lint rule that gathers information from different modules before performing a final analysis to determine if there are errors.

Writing tests for files that reside in the same module generally follow the same principles as outlined in my post Enforcing Team Rules with Lint: Tests so for now we will be focusing on writing tests for a multi-module setup.

We will write a test with the following set-up:

two modules, a library and an app module
the library module holds a colors_deprecated.xml file
the app module holds a layout file that uses one of the deprecated colours

Let’s set up the colors_deprecated.xml file:

val DEPRECATED_COLOUR_FILE: TestFile = xml(
    "res/values/colors_deprecated.xml",
    """
        <resources>
            <color name="red_error">#d6163e</color>
            <color name="another_value">#d6163e</color>
            <color name="and_another_value">#d6163e</color>
            </resources>
    """
).indented()

And the layout file consuming the colour:

val VIEW_WITH_DEPRECATED_COLOUR: TestFile = xml(
    "res/layout/layout.xml",
    """
        <View xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:background="@color/red_error" />
    """
).indented()

Next we need to set up our projects (aka modules). Lint’s mechanism for setting modules up in tests is via ProjectDescription (oddly enough this is missing in the API guide as well ). Let’s set up the library module first:

val deprecatedModule = ProjectDescription()
    .name("deprecated-library")
    .type(ProjectDescription.Type.LIBRARY)
    .files(DEPRECATED_COLOUR_FILE)

Here we provide the module name, declare it as a library, and include the files that should be in the module.

Let’s then set up our app module:

val appModule = ProjectDescription()
    .name("app")
    .files(VIEW_WITH_DEPRECATED_COLOUR)
    .dependsOn(deprecatedModule)

Note that we call dependsOn here to link the two modules together.

All that’s left to do now is to write the bit that runs the test:

lint()
    // Add modules to the test task
    .projects(deprecatedModule, appModule)
    // Tells Lint to analyse all modules first before reporting issues
    .testModes(TestMode.PARTIAL)
    .run()
    .expect(
        """
        res/layout/layout.xml:4: Error: Deprecated colours should not be used [DeprecatedColorInXml]
            android:background="@color/red_error" />
                                ~~~~~~~~~~~~~~~~
            1 errors, 0 warnings
        """
    )

Using the same principles we can write tests for analysing transitive dependencies as well. For the full test suite for this Lint rule, check out the source code on Github.

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