Value Matchers in Expresso Intents

After the decision of using Crashlytics for our first pilot (Education for ethopia), the tech team discovered that one particular crash was redundant. This crash was due to a malformed Intent between the video player in portrait mode and the video player in landscape mode.


To understand a little bit more about the problem faced later, I want to describe briefly how this transition of video player mode is working for us.


This activity handles the playlist of videos and the video player (we use ExoPlayer).


This activity handles only the video player and has a locked screenOrientation in the AndroidManifest:


The behavior

Our expected behavior is that depending on 3 attributes of the player (currentPosition, currentMediaItem.mediaId, isPlaying), the user find the video in the same state switching from Portrait to Landscape or from Landscape to Portrait.


Now, because we had this redundant crash, we decided to do like all the good engineers: testing. With that we would then be able to prevent these crashes to ever happen again in the future.

For that, we used the Espresso Intent extension and basically check the extras passed between activities. To do that we did the following:

activityRule.scenario.onActivity {
    val player = it.findViewById<PlayerView>(!!

    player.pause() // pause the video
    player.seekTo(1000) // we seek to 1 sec from the beginning

        hasExtra(CURRENT_POSITION, 1000L), // 1 sec
        hasExtra(MEDIA_ID, "A_VIDEO.mp4"),
        hasExtra(IS_PLAYING, false) // is not playing

pretty simple and pretty expressive code.

The real trouble came when we decided to test a video that is playing. The first problem came from ExoPlayer itself, we basically needed to wait that the video was in playing state before to even create the new activity. To do that we added a listener like the following:

player.addListener(object: Player.EventListener {
    override fun onIsPlayingChanged(playing: Boolean) {
        isPlaying = playing

and we basically waited for isPlaying to change:

while (!isPlaying && deadline.isNotExceeded()) {}

After that we were able to click our full_screen_button and we were ready to check our intents. In a naive attempte we wrote something like:

        hasExtra(CURRENT_POSITION, greaterThanOrEqualTo(1000L)), // >= 1000 because playing
        hasExtra(MEDIA_ID, "A_VIDEO.mp4"),
        hasExtra(IS_PLAYING, true)

And we thought “yeah looks like it’s gonna work”. But after running our test, we received a ❌. We then decided to read the Logs and see what wouldn’t match. I let you judge by yourself:

IntentMatcher: (has extras: has bundle with: key: is "current_position" value: is <a value equal to or greater than <1000L>> and has extras: has bundle with: key: is "media_id" value: is "A_VIDEO.mp4" and has extras: has bundle with: key: is "is_playing" value: is <true>)

Matched intents:[]

Recorded intents:
-Intent { cmp=com.clementjean.unittest/.NewActivity (has extras) } handling packages:[[com.clementjean.unittest]], extras:[Bundle[{current_position=1158, media_id=A_VIDEO.mp4, is_playing=true}]])

Apparently the recorded intent is matching, we have a current_position >= 1000, we have the right meta_id and the is_playing is set to true. Correct right?

After an hour of trying to debug that, we checked the documentation (we only scanned through it before) and we finally found what was the problem.

In the documentation of Intent matchers, we can see that there are two definitions of the function hasExtra:

Matcher<Intent> hasExtra (Matcher<String> keyMatcher, Matcher<?> valueMatcher)


Matcher<Intent> hasExtra (String key, T value)

Do you see the problem?

The problem is in that line hasExtra(CURRENT_POSITION, greaterThanOrEqualTo(1000L)) because by using the string CURRENT_POSITION, we were actually using the second overload of the function and thus the value of our Intent extra was definitely not equal to value matcher greaterThanOrEqualTo.

To solve that we need to add the matcher is() around the string CURRENT_POSITION and we would then access the first definition of the matcher hasExtra. It gives us something like:

        hasExtra(`is`(CURRENT_POSITION), greaterThanOrEqualTo(1000L)),
        hasExtra(MEDIA_ID, "A_VIDEO.mp4"),
        hasExtra(IS_PLAYING, true)

The problem

For me the problem is the impossibility for library designers to define a certain domain for the template parameter. Knowing that an intent only accept a restricted amount of types as extra, it would be great to have the possibility to only constraint the template to these types. This is however a language design problem and it might not be solved in a near future (if you are a language developer though, you might consider solving this).


Beware function overloads

Written on February 15, 2021