testing: add RUNS_PER_TEST environment variable (#230)

This is a change equivalent to:
googleapis/google-cloud-cpp-spanner#1360

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Author: Takashi Matsuo

ci/kokoro/docker/build-in-docker-bazel.sh

@@ -46,6 +46,10 @@ echo "Using Bazel in ${BAZEL_BIN}"
 echo "================================================================"
 
 bazel_args=("--test_output=errors" "--verbose_failures=true" "--keep_going")
+if [[ -n "${RUNS_PER_TEST}" ]]; then
+    bazel_args+=("--runs_per_test=${RUNS_PER_TEST}")
+fi
+
 if [[ -n "${BAZEL_CONFIG}" ]]; then
     bazel_args+=("--config" "${BAZEL_CONFIG}")
 fi

ci/kokoro/docker/build-in-docker-cmake.sh

@@ -140,6 +140,11 @@ _EOF_
   fi
 fi
 
+ctest_args=("--output-on-failure")
+if [[ -n "${RUNS_PER_TEST}" ]]; then
+    ctest_args+=("--repeat-until-fail" "${RUNS_PER_TEST}")
+fi
+
 if [[ "${BUILD_TESTING:-}" = "yes" ]]; then
   # When the user does a super-build the tests are hidden in a subdirectory.
   # We can tell that ${BINARY_DIR} does not have the tests by checking for this
@@ -150,7 +155,7 @@ if [[ "${BUILD_TESTING:-}" = "yes" ]]; then
     echo
     echo "${COLOR_YELLOW}Running unit tests $(date)${COLOR_RESET}"
     echo
-    (cd "${BINARY_DIR}" && ctest --output-on-failure)
+    (cd "${BINARY_DIR}" && ctest "${ctest_args[@]}")
 
     echo
     echo "${COLOR_YELLOW}Completed unit tests $(date)${COLOR_RESET}"

ci/kokoro/docker/build.sh

@@ -402,6 +402,10 @@ docker_flags=(
     # produces properly colorized error messages.
     "--env" "TERM=${TERM:-dumb}"
 
+    # If set, add a flag --runs_per_test=<value> to bazel or --repeat-until-fail
+    # to ctest.
+    "--env" "RUNS_PER_TEST=${RUNS_PER_TEST:-}"
+
     # Tells scripts whether they are running as part of a CI or not.
     "--env" "RUNNING_CI=${RUNNING_CI:-no}"