How can I test setResult() in an Android Espresso test?

this works for me:

@Test
    fun testActivityForResult(){

        // Build the result to return when the activity is launched.
        val resultData = Intent()
        resultData.putExtra(KEY_VALUE_TO_RETURN, true)

        // Set up result stubbing when an intent sent to <ActivityB> is seen.
        intending(hasComponent("com.xxx.xxxty.ActivityB")) //Path of <ActivityB>
            .respondWith(
                Instrumentation.ActivityResult(
                    RESULT_OK,
                    resultData
                )
            )

        // User action that results in "ActivityB" activity being launched.
        onView(withId(R.id.view_id))
            .perform(click())

      // Assert that the data we set up above is shown.
     onView(withId(R.id.another_view_id)).check(matches(matches(isDisplayed())))
    }

Assuming a validation like below on onActivityResult(requestCode: Int, resultCode: Int, data: Intent?)

if (requestCode == REQUEST_CODE && resultCode == Activity.RESULT_OK) {

    data?.getBooleanExtra(KEY_VALUE_TO_RETURN, false)?.let {showView ->
                if (showView) {
                 another_view_id.visibility = View.VISIBLE
                }else{
                 another_view_id.visibility = View.GONE
                 }
            }
        }

I follow this guide as reference : https://developer.android.com/training/testing/espresso/intents and also i had to check this links at the end of the above link https://github.com/android/testing-samples/tree/master/ui/espresso/IntentsBasicSample and https://github.com/android/testing-samples/tree/master/ui/espresso/IntentsAdvancedSample

If you are willing to upgrade to 2.1, then take a look at Espresso-Intents:

Using the intending API (cousin of Mockito.when), you can provide a response for activities that are launched with startActivityForResult

This basically means it is possible to build and return any result when a specific activity is launched (in your case the BarActivity class).

Check this example here: https://google.github.io/android-testing-support-library/docs/espresso/intents/index.html#intent-stubbing

And also my answer on a somewhat similar issue (but with the contact picker activity), in which I show how to build a result and send it back to the Activity which called startActivityForResult()

If meanwhile you switched to the latest Espresso, version 3.0.1, you can simply use an ActivityTestRule and get the Activity result like this:

assertThat(rule.getActivityResult(), hasResultCode(Activity.RESULT_OK));
assertThat(rule.getActivityResult(), hasResultData(IntentMatchers.hasExtraWithKey(PickActivity.EXTRA_PICKED_NUMBER)));

You can find a working example here.