Improve pytest speend by grouping 20 tests together. (#2390)

*Improve pytest speed by grouping 20 tests together

Author: mint570

.azure-pipelines/test-docker-sonic-vs-template.yml

@@ -71,16 +71,32 @@ jobs:
       if [ '${{ parameters.archive_gcov }}' == True ]; then
         all_tests=$(ls test_*.py)
         all_tests="${all_tests} p4rt"
+        test_set=()
+        # Run 20 tests as a set.
         for test in ${all_tests}; do
-          test_name=$(echo "${test}" | cut -d "." -f 1)
-          sudo py.test -v --force-flaky --junitxml="${test_name}_tr.xml" --keeptb --imgname=docker-sonic-vs:$(Build.DefinitionName).$(Build.BuildNumber) ${test}
+          test_set+=("${test}")
+          if [ ${#test_set[@]} -ge 20 ]; then
+            test_name=$(echo "${test_set[0]}" | cut -d "." -f 1)
+            echo "${test_set[*]}" | xargs sudo py.test -v --force-flaky --junitxml="${test_name}_tr.xml" --keeptb --imgname=docker-sonic-vs:$(Build.DefinitionName).$(Build.BuildNumber)
+            container_count=$(docker ps -q -a | wc -l)
+            if [ ${container_count} -gt 0 ]; then
+              ./gcov_support.sh set_environment $(Build.ArtifactStagingDirectory)
+              docker stop $(docker ps -q -a)
+              docker rm $(docker ps -q -a)
+            fi
+            test_set=()
+          fi
+        done
+        if [ ${#test_set[@]} -gt 0 ]; then
+          test_name=$(echo "${test_set[0]}" | cut -d "." -f 1)
+          echo "${test_set[*]}" | xargs sudo py.test -v --force-flaky --junitxml="${test_name}_tr.xml" --keeptb --imgname=docker-sonic-vs:$(Build.DefinitionName).$(Build.BuildNumber)
           container_count=$(docker ps -q -a | wc -l)
           if [ ${container_count} -gt 0 ]; then
             ./gcov_support.sh set_environment $(Build.ArtifactStagingDirectory)
             docker stop $(docker ps -q -a)
             docker rm $(docker ps -q -a)
           fi
-        done
+        fi
       else
         sudo py.test -v --force-flaky --junitxml=tests_tr.xml --imgname=docker-sonic-vs:$(Build.DefinitionName).$(Build.BuildNumber)
       fi