Add Kotlin unit test infrastructure and CircleCI step (#159)

* chore: add Kotlin unit test dependencies to build.gradle

Add JUnit 4, Mockito, and OkHttp MockWebServer as test dependencies.
These are needed to run the existing ExponentialRetryInterceptorTest and
future interceptor tests.

Co-authored-by: Claude <claude@anthropic.com>

* chore: add Kotlin unit test infrastructure and CI step

- Add JUnit 4, Mockito, and OkHttp MockWebServer to android/build.gradle
  test dependencies
- Add standalone test-runner project with Gradle wrapper for running
  Kotlin unit tests independently of the React Native build
- Add kotlin-tests job to CircleCI using cimg/android executor
- Add smoke test to verify the test infrastructure works
- Wire kotlin-tests into the build workflow as a gate for build-package

This enables TDD for Android interceptor code without requiring a full
React Native app build.

Co-authored-by: Claude <claude@anthropic.com>

* fix: wrap MockWebServer and Response in use{} blocks in SmokeTest

Address CodeRabbit review: prevent resource leaks if assertions fail
by using Kotlin's use{} for automatic cleanup of MockWebServer and
Response objects.

Co-authored-by: Claude <claude@anthropic.com>

---------

Co-authored-by: Claude <claude@anthropic.com>

Author: pavelzeman

.circleci/config.yml

@@ -5,6 +5,10 @@ executors:
     docker:
       - image: circleci/node:14
     working_directory: ~/project
+  android:
+    docker:
+      - image: cimg/android:2024.01
+    working_directory: ~/project
 
 commands:
   attach_project:
@@ -62,6 +66,21 @@ jobs:
           path: coverage
           destination: coverage
 
+  kotlin-tests:
+    executor: android
+    steps:
+      - checkout
+      - run:
+          name: Run Kotlin unit tests
+          command: |
+            cd test-runner
+            ./gradlew test
+      - store_test_results:
+          path: test-runner/build/test-results
+      - store_artifacts:
+          path: test-runner/build/reports/tests
+          destination: kotlin-test-reports
+
   build-package:
     executor: default
     steps:
@@ -105,12 +124,14 @@ workflows:
       - unit-tests:
           requires:
             - install-dependencies
+      - kotlin-tests
       - build-package:
           requires:
             - install-dependencies
             - lint
             - typescript
             - unit-tests
+            - kotlin-tests
       - release:
           context: mattermost-rn-libraries
           requires:

android/build.gradle

@@ -65,4 +65,8 @@ dependencies {
   implementation "com.squareup.okhttp3:okhttp-tls:4.12.0"
   implementation "com.squareup.okhttp3:okhttp-urlconnection:4.12.0"
   implementation "androidx.datastore:datastore-preferences:1.1.1"
+
+  testImplementation "junit:junit:4.13.2"
+  testImplementation "org.mockito:mockito-core:5.11.0"
+  testImplementation "com.squareup.okhttp3:mockwebserver:4.12.0"
 }

test-runner/build.gradle.kts

@@ -0,0 +1,21 @@
+plugins {
+    kotlin("jvm") version "1.9.22"
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation("com.squareup.okhttp3:okhttp:4.12.0")
+    testImplementation("junit:junit:4.13.2")
+    testImplementation("com.squareup.okhttp3:mockwebserver:4.12.0")
+}
+
+sourceSets {
+    test {
+        kotlin {
+            srcDir("src/test/kotlin")
+        }
+    }
+}

test-runner/gradle/wrapper/gradle-wrapper.jar

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.5-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists