title: How to specify unit test folder in two-dimension flavor
body: <p>I had a project that have two-dimension flavor.
  e.g. flavorDimensions "device", "fruit"</p>
  
  <ol>
  <li>mobileBanana</li>
  <li>mobileApple</li>
  <li>stbBanana</li>
  <li>stbApple</li>
  </ol>
  
  <p>All building result is fine, and I want to put unit test only for <strong>stbApple</strong> when select <strong>Build Variant</strong> in Android Studio.
  How to achieve this goal ?</p>
  
  <p>I had tried below experiment, but still fail.</p>
  
  <p>1.Set sourceSets (fail, other build variant still run this folder)</p>
  
  <pre><code>sourceSets {
          mobile {
              assets.srcDirs = ['src/mobile/assets']
          }
  
          stbApple {
              androidTest {
                  // Other build variant still run unit test in this folder.......
                  java.srcDirs += ['src/androidTestStbApple/java']
              }
          }
      }
  </code></pre>
  
  <p>2.Give androidTestStbApple folder in src folder, as <a href="http://tools.android.com/tech-docs/unit-testing-support#TOC-Flavors-and-build-types-support" rel="nofollow">doc</a> said, we would not give specified folder in Gradle, it can distinguish build variant by folder.
  and the result is failed,too.</p>
  
  <p>It seems two-dimension flavor is not supported in gradle / android studio now for unit testing. (one-dimension can work successfully)</p>