Allow tests execution on environments there Android SDK is not installed

Author: macisamuele

samples/junit-tests/build.gradle

@@ -1,21 +1,10 @@
 plugins {
-    id("com.android.library")
-    id("kotlin-android")
+    id("kotlin")
     id("com.yelp.codegen.plugin")
     id("io.gitlab.arturbosch.detekt")
     id("kotlin-kapt")
 }
 
-android {
-    compileSdkVersion = 28
-    defaultConfig {
-        minSdkVersion 21
-        targetSdkVersion 28
-        versionCode = 1
-        versionName = "1.0"
-    }
-}
-
 dependencies {
     // Kotlin
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.70"

samples/junit-tests/src/main/AndroidManifest.xml

@@ -17,10 +17,24 @@ pluginManagement {
     }
 }
 
-include(
-        ":samples:junit-tests",
+include(":samples:junit-tests")
+
+if (isAndroidSDKConfigured()) {
+    include(
         ":samples:kotlin-android",
         ":samples:kotlin-coroutines",
-        ":samples:groovy-android")
+        ":samples:groovy-android"
+    )
+}
 
 includeBuild("gradle-plugin")
+
+fun isAndroidSDKConfigured(): Boolean {
+    if (System.getenv("ANDROID_SDK_ROOT") != null) {
+        return true;
+    }
+    // TODO: Check if `sdk.dir` property is defined in `local.properties`
+
+    // Ensure that on CI systems we do assume that Android is installed
+    return System.getenv("CI") != null;
+}