There are several methods of unit testing in Android, what's the best one for testing a custom view I've written?

I'm currently testing it as pa开发者_如何学Pythonrt of my activity in an instrumentation test case, but I'd rather test just the view, isolated.

A simple solution for the lack of a View-focused TestCase implementation would be to create a simple Activity within your test project that includes your view. This will allow you to write tests against the view using a simple Activity. Information on Activity testing:

http://developer.android.com/reference/android/test/ActivityUnitTestCase.html

As mentioned in wikibooks:

unit testing is a method by which individual units of source code are tested to determine if they are fit for use.

So when you say you want to test your custom view, you can check various methods of your custom views like "onTouchEvent", "onDown", "onFling", "onLongPress", "onScroll", "onShowPress", "onSingleTapUp", "onDraw" and various others depending on your business logic. You can provide mock values and test it. I would suggest two methods of testing your custom view.

1) Monkey Testing

Monkey testing is random testing performed by automated testing tools.

_{G.D.S. Prasad on geekinterview.com}

and:

A monkey test is a unit test that runs with no specific test in mind. The monkey in this case is the producer of any input. For example, a monkey test can enter random strings into text boxes to ensure handling of all possible user input or provide garbage files to check for loading routines that have blind faith in their data.

_{sridharrganesan on geekinterview.com}

This is a black box testing technique and it can check your custom view in so many unique conditions that you will get astonished :) .

2) Unit Testing

2a) Use Robotium Unit Testing Framwork

Go to Robotium.org or http://code.google.com/p/robotium/ and download the example test project. Robotium is a really easy to use framework that makes testing of android applications easy and fast. I created it to make testing of advanced android applications possible with minimum effort. Its used in conjunction with ActivityInstrumentationTestCase2.

2b) Use Android Testing Framework

Here are the links to the reference: http://developer.android.com/reference/android/test/ActivityInstrumentationTestCase2.html and http://developer.android.com/reference/android/test/ActivityUnitTestCase.html

For starters: http://developer.android.com/guide/topics/testing/testing_android.html

According to one user : Aside from easily testing non platform dependent logic I haven't found a clever way to run tests, so far (at least for me) any actual platform logic testing is cumbersome. It's almost non trivial anyway because I've found differences in implementation between the emulator and my actual device and I hate to run a unit test implementation on my device just to remove the application afterwards.

My strategy has been: Try to be concise and make the logic well thought out and then test implementation piece by piece (less then desirable).

Also Stephen Ng provides good aproach for real Unit Test for Android projects solution: https://sites.google.com/site/androiddevtesting/

One user has made a screencast.

Here's a ScreenCast I made on how I got Unit Tests to work. Simple Unit Tests and more complex unit tests that depend on having a reference to Context or Activity objects. http://www.gubatron.com/blog/2010/05/02/how-to-do-unit-testing-on-android-with-eclipse/

Hope it helps you testing your custom view in all possible conditions :)

Comment (futlib) All your suggestions seem to involve testing the ACTIVITY, while I really want to test just the VIEW. I might want to use this view in other activities, so it doesn't make much sense for me to test it with a specific one. – futlib

Answer: To implement a custom view, you will usually begin by providing overrides for some of the standard methods that the framework calls on all views. For example "onDraw", "onKeyDown(int, KeyEvent)", "onKeyUp(int, KeyEvent)", "onTrackballEvent(MotionEvent)" etc of your custom view. So when you want to do unit testing for your custom you'll have to test these methods, and provide mock values to it so that you can test your custom view on all possible cases. Testing these methods doesn't mean that you are testing your ACTIVITY, but it means testing your custom view (methods/functions) which is within an activity. Also you'll have to put your custom view in an Activity eventually for your target users to experience it. Once thoroughly tested , your custom view can be placed in many projects and many activities.

Here's a different suggestion which works fine in many cases: Assuming you are referencing your custom view from within a layout file, you can use an AndroidTestCase, inflate the view, and then perform tests against it in isolation. Here's some example code:

my_custom_layout.xml:

<?xml version="1.0" encoding="utf-8"?>
<de.mypackage.MyCustomView ...

MyCustomView.java:

public class MyCustomView extends LinearLayout {

    public MyCustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public void setTitle(CharSequence title) {
        ((TextView) findViewById(R.id.mylayout_title_textView)).setText(title);
    }
...

MyCustomViewTest.java:

public class MyCustomViewTest extends AndroidTestCase {

    private MyCustomView customView;

    @SuppressLint("InflateParams")
    @Override
    protected void setUp() throws Exception {
        super.setUp();
        customView = (MyCustomView) LayoutInflater.from(getContext())
            .inflate(R.layout.my_custom_layout, null);
    }

    public void testSetTitle_SomeValue_TextViewHasValue() {
        customView.setTitle("Some value");
        TextView titleTextView = (TextView) valueSelection.findViewById(R.id.mylayout_title_textView);
        assertEquals("Some value", titleTextView.getText().toString());
    }
...

I struggled a lot to set up screenshot tests for my custom view.
Here is how I managed to do that and everything I learned in the process.
It may not be the most convenient method, but I put it here anyway.
And of course, screenshot testing is now a little bit easier in Jetpack Compose.

⚠ Caution #1

You can use JUnit 4 if you want. I'm using JUnit 5. Because JUnit 5 is built on Java 8 from the ground up, its instrumentation tests will only run on devices running Android 8.0 (API 26) or newer. Older phones/emulators will skip the execution of these tests completely, marking them as ignored.

If you want to run JUnit 5 tests on Android, refer to this answer for how to set it up.

⚠ Caution #2

The screenshot tests may not work on other devices even if they have the same screen DPI (they may not work at all on devices with different screen DPIs). For example, even when I use the same device in my local machine and on GitHub Actions to run the tests, they do not produce the same result (GitHub Actions assertions fail). So, I had to disable them on GitHub Actions.

If you want to disable the screenshot tests on GitHub Actions (or other CI), see this answer.

⚠ Caution #3

If you have resources in instrumented tests (in androidTest source set) and you want to reference their id, you should use them like this (note the package name followed by .test):

com.example.test.R.id.an_id

For example, if your package name is my.package.name then to access the layout file in src/androidTest/res/layout/my_layout.xml in your tests, you use my.package.name.test.R.layout.my_layout.

⚠ Caution #4

Since we are saving our test screenshots on the external storage of the device/emulator, we need to make sure that we have both WRITE_EXTERNAL_STORAGE permission added in the manifest and adb install options -g and -r configured in the build script. When running on Marshmallow+, we also need to have those permissions granted before running a test. -g is for granting permissions when installing the app (works on Marshmallow+ only) while -r is to allow reinstalling of the app. These correspond to adb shell pm install options. Just be aware that this does not work with Android Studio yet.

So, create an AndroidManifest.xml file in src/androidTest/ directory and add the following to it:

<manifest package="my.package.name">
  <!-- For saving screenshots in tests -->
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"
                   tools:ignore="ScopedStorage"
                   tools:remove="android:maxSdkVersion"/>
  <application android:requestLegacyExternalStorage="true">
    <activity android:name=".MyActivityThatContainsTheView"/>
  </application>
</manifest>

and add the adb install options in your library Gradle build file:

android {
    // Note that adbOptions block is deprecated in Android Gradle Plugin 7.0.0;
    // replace adbOptions block with installation block
    adbOptions {
        installOptions("-g", "-r")
    }
}

⚠ Caution #5

I save the reference screenshot (the one I want to compare with the current screenshot) in src/androidTest/assets directory. So, specify that directory as an assets entry in the library build file:

android {
    sourceSets {
        // This is Kotlin DSL; see https://stackoverflow.com/a/59920318 for groovy DSL
        get("debug").assets.srcDirs("src/androidTest/assets")
    }

⚠ Caution #6

To pass instrumentation arguments when running the tests (like shouldSave in my code), do this:

• For a Gradle task:
  • Running the task from command line: pass your arguments after the task name
    ./gradlew myTask -Pandroid.testInstrumentationRunnerArguments.shouldSave=true
  • Running the task with Studio: pass your arguments in run config Arguments: field
    -Pandroid.testInstrumentationRunnerArguments.shouldSave=true
• For an Android Studio Android Instrumented Tests run configuration:
  Select Edit Configurations... from run configuration popup, then select your run configuration, click ... in front of Instrumentation arguments: field and then add a name-value entry like Name shouldSave Value true.

See this article and this post.

⚠ Caution #7

The first time you want to run the screenshot tests and also whenever you update your custom view that might change its visuals, you should run the tests passing true for shouldSave argument so the new screenshots are saved in the device (see comments above save method in code below for the location of the images) and then manually copy the new screenshots to your src/androidTest/assets/ directory so they will be the new reference ones.

⚠ Caution #8

Make sure to use -ktx versions of androidx libraries (like AndroidX Core library) for Kotlin.
The -ktx variants contain useful Kotlin extension functions. Example:

implementation("androidx.core:core-ktx:1.6.0")

⚠ Caution #9

Make sure the device screen is on and unlocked for the activity to go to resumed state.

The code

This is my test activity in src/androidTest/java/com/example/ directory that exposes the view that I want to take its screenshot as a property:

class MyActivityThatContainsTheView : AppCompatActivity() {

    lateinit var myView: MyView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(my.package.name.test.R.layout.my_layout_that_contains_the_view)
        myView = findViewById(my.package.name.test.R.id.my_view_id_in_the_layout_file)
    }
}

And finally, this is my tests and how I save, load, and compare the screenshots:

@DisabledIfBuildConfigValue(named = "CI", matches = "true")
class ScreenshotTestView {

    @JvmField
    @RegisterExtension
    val scenarioExtension = ActivityScenarioExtension.launch<MyActivityThatContainsTheView>()
    lateinit var scenario: ActivityScenario<MyActivityThatContainsTheView>
    // See ⚠ Caution #6 above in the post
    val shouldSave = InstrumentationRegistry.getArguments().getString("shouldSave", "false").toBoolean()
    val shouldAssert = InstrumentationRegistry.getArguments().getString("shouldAssert", "true").toBoolean()

    @BeforeEach fun setUp() {
        scenario = scenarioExtension.scenario
        scenario.moveToState(Lifecycle.State.RESUMED)
    }

    @Test fun test1() {
        val screenshotName = "screenshot-1"
        scenario.onActivity { activity ->
            val view = activity.myView
            view.drawToBitmap()
                    .saveIfNeeded(shouldSave, screenshotName)
                    .assertIfNeeded(shouldAssert, screenshotName)
        }
    }

    fun Bitmap.saveIfNeeded(shouldSave: Boolean, name: String): Bitmap {
        if (shouldSave) save(name)
        return this
    }
    
    fun Bitmap.assertIfNeeded(shouldCompare: Boolean, screenshotName: String) {
        if (shouldCompare) assert(screenshotName)
    }
    
    /**
     * The screenshots are saved in /Android/data/my.package.name.test/files/Pictures
     * on the external storage of the device.
     */
    private fun Bitmap.save(name: String) {
        val context = InstrumentationRegistry.getInstrumentation().targetContext
        val path = context.getExternalFilesDir(Environment.DIRECTORY_PICTURES)
        val file = File(path, "$name.png")
        file.outputStream().use { stream ->
            compress(Bitmap.CompressFormat.PNG, 100, stream)
        }
    }
    
    private fun Bitmap.assert(screenshotName: String) {
        val reference = loadReferenceScreenshot(screenshotName)
        // I'm using AssertJ library; you can simply use assertTrue(this.sameAs(reference))
        assertThat(this.sameAs(reference))
            .withFailMessage { "Screenshots are not the same: $screenshotName.png" }
            .isTrue()
    }
    
    private fun loadReferenceScreenshot(name: String): Bitmap {
        val context = InstrumentationRegistry.getInstrumentation().context
        val assets = context.resources.assets
        val reference = assets.open("$name.png").use { stream ->
            BitmapFactory.decodeStream(stream)
        }
        return reference
    }
}