[android] #3708 - added code coverage test documentation and debug option

platform/android/MapboxGLAndroidSDKTestApp/build.gradle

@@ -59,6 +59,10 @@ android {
     }
 
     buildTypes {
+        debug{
+            // run code coverage reports
+            testCoverageEnabled = true
+        }
         release {
             minifyEnabled false
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

platform/android/tests/docs/UI_TESTS.md

@@ -1,5 +1,5 @@
 #UI Tests
-## Running Espresso tests locally on a device
+## Running Espresso tests locally
 
 This test project comes with all the required Android Testing Support Library dependencies
 in the Gradle file. Tests are under the `app/src/androidTest` folder.
@@ -19,7 +19,7 @@ To create a new run configuration:
 
 You can now run this configuration from the main toolbar dropdown menu.
 
-## Running Espresso tests manually on AWS Device Farm
+## Running Espresso tests on AWS Device Farm
 
 On a terminal, within `mapbox-gl-native/android/java`,
 run the tests (`cC` stands for `connectedCheck`):
@@ -42,6 +42,22 @@ On Step 2, you can also separate by commas different classes: `com.mapbox.mapbox
 If you have no tests for your app, or want to test some random user behaviour,
 you can just choose "Built-in: Fuzz" in step 2.
 
+### Code coverage
+You can generate JaCoCo reports from espresso tests by
+
+- adding this to build.gradle:
+
+ ```java
+ buildTypes {
+        debug {
+           // Run code coverage reports by default on debug builds.
+          testCoverageEnabled = true
+        }
+}
+```
+
+- running the gradle task `createMockDebugCoverageReport` when executing tests.
+
 ## Running Espresso test automatically on AWS Device Farm
 To automatically execute Espresso tests as part of our CI build, we have created a Python [script](https://github.com/mapbox/mapbox-gl-native/blob/aws-devicelab/android/scripts/devicefarm.py).
 
@@ -129,3 +145,6 @@ This script is responsible for:
     --test-apk-path TEST_APK_PATH
                           Path to the tests APK (default: None)
   ```
+
+
+

platform/android/tests/docs/UNIT_TESTS.md

@@ -20,6 +20,14 @@ You can also run the tests from the command line with:
 $ ./gradlew test --continue -p MapboxGLAndroidSDKTestApp
 ```
 
+### Code Coverage
+Showing code coverage directly in the IDE.
+- Switch your Build Variant to the Unit Tests artifact
+- Right click a unit test and select `Run test with coverage`
+- Select `Add to active suites` //this will create a run configuration
+- Edit the run configuration to include/exclude packages in the `Code coverage`-tab.
+
+
 ## Running Unit tests on CI
 The Unit tests are executed as part of the build process on our CI and are 
 automatically run for each new commit pushed to this repo. If a Unit tests