Change test to import pyext._message

appveyor.yml

@@ -126,7 +126,7 @@ test_script:
     - mkdir for_testing
     - cd for_testing
     - python --version
-    - python -c "import google.protobuf;"
+    - python -c "from google.protobuf.pyext import _message;"
     - cd ..
 
 artifacts:

config.sh

@@ -53,5 +53,5 @@ function build_wheel {
 function run_tests {
     # Runs tests on installed distribution from an empty directory
     python --version
-    python -c "import google.protobuf;"
+    python -c "from google.protobuf.pyext import _message;"
 }