[in_app_purchase] moved android iap unit tests (flutter#3732)

packages/in_app_purchase/in_app_purchase/android/build.gradle

@@ -31,12 +31,17 @@ android {
     lintOptions {
         disable 'InvalidPackage'
     }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
 }
 
 dependencies {
     implementation 'androidx.annotation:annotation:1.0.0'
     implementation 'com.android.billingclient:billing:3.0.2'
     testImplementation 'junit:junit:4.12'
+    testImplementation 'org.json:json:20180813'
     testImplementation 'org.mockito:mockito-core:3.6.0'
     androidTestImplementation 'androidx.test:runner:1.1.1'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'

packages/in_app_purchase/in_app_purchase/android/src/test/java/android/text/TextUtils.java

@@ -0,0 +1,11 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package android.text;
+
+public class TextUtils {
+  public static boolean isEmpty(CharSequence str) {
+    return str == null || str.length() == 0;
+  }
+}

packages/in_app_purchase/in_app_purchase/android/src/test/java/android/util/Log.java

@@ -0,0 +1,27 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package android.util;
+
+public class Log {
+  public static int d(String tag, String msg) {
+    System.out.println("DEBUG: " + tag + ": " + msg);
+    return 0;
+  }
+
+  public static int i(String tag, String msg) {
+    System.out.println("INFO: " + tag + ": " + msg);
+    return 0;
+  }
+
+  public static int w(String tag, String msg) {
+    System.out.println("WARN: " + tag + ": " + msg);
+    return 0;
+  }
+
+  public static int e(String tag, String msg) {
+    System.out.println("ERROR: " + tag + ": " + msg);
+    return 0;
+  }
+}