Test Error - NoClassDefFoundError: Failed resolution of: Lorg/hamcrest/Matchers

Question

I am using Espresso for Instrumented Test but got this error on the Stack Trace:

The error being caused by a missing class as shown below:

Caused by: java.lang.ClassNotFoundException: Didn't find class "org.hamcrest.Matchers" on path: DexPathList[[zip file "/system/framework/android.test.runner.jar", zip file "/system/framework/android.test.mock.jar", zip file "/system/framework/android.test.base.jar", zip file "/data/app/~~vnZzxGNKnS4V6YkEf4falA==/com.example.android.architecture.blueprints.reactive.test-K_x0_yJ0hJeDHaJkDmHXRw==/base.apk", zip file "/data/app/~~oeYx2MgTcILbk-vq_WPx1A==/com.example.android.architecture.blueprints.reactive-0wMHYEe95hx_1cnbdAoZAw==/base.apk"],nativeLibraryDirectories

It first occurred immediately after I added this code in the Fragment Test:

These are my relevant Libs on the Gradle:

I have these imports:

import androidx.fragment.app.testing.launchFragmentInContainer
import androidx.test.espresso.Espresso.onView
import androidx.test.espresso.assertion.ViewAssertions.matches
import androidx.test.espresso.matcher.ViewMatchers.*
import androidx.test.ext.junit.runners.AndroidJUnit4
import org.hamcrest.core.IsNot.not

Answer 1

TLDR answer, you don't need to downgrade the whole espresso setup there is a Hamcrest version conflict with transitive dependencies which can be easily solved:

If you are using:

androidTestImplementation 'androidx.test.espresso:espresso-contrib:3.4.0'

//change it to:
androidTestImplementation 'androidx.test.espresso:espresso-contrib:3.3.0'

if you are using:

androidTestImplementation 'androidx.test.espresso:espresso-accessibility:3.4.0'

//change it to:
androidTestImplementation "androidx.test.espresso:espresso-accessibility:3.3.0"

You should still be able to keep espresso core at the higher 3.4.0 version

---

If you want to understand, here is the longer explanation:

To see what is going on under the hood we can use the dependencies gradle task to print out the dependency tree, in android studio terminal:

./gradlew :app:dependencies

We can run it twice, using the dependencies at the two version levels and can check the differences.

• At several points there are requests for hamcrest libraries version 1.3 which match most of the common android dependencies.
• On the left side (dependency tree for v3.3.0) every hamcrest transitive dependency is provided as requested, no surprise it works!
• On the right side (dependency tree for v3.4.0) we can see some of the requests got "substitute" hamcrest libraries at a higher version which, in this case, does not work.

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