Android Studio

Error:
Could not resolve all dependencies for configuration ':app:_debugUnitTestCompile

It can happen if you have proxy settings and you are not connected to it.

Create and Edit gradle.properties

C:\Users\NAME\.gradle\.gradle.properties

systemProp.http.proxyHost=www.somehost.org
systemProp.http.proxyPort=8080
systemProp.http.proxyUser=userid
systemProp.http.proxyPassword=password
systemProp.http.nonProxyHosts=*.nonproxyrepos.com|localhost    

systemProp.https.proxyHost=www.somehost.org
systemProp.https.proxyPort=8080
systemProp.https.proxyUser=userid
systemProp.https.proxyPassword=password
systemProp.https.nonProxyHosts=*.nonproxyrepos.com|localhost

other:
1.Download gradle
2.untar and set  gradle home dir in Android Audio
  C:\Program Files\Android\Android Studio\gradle\gradle-x.x