ci: fail a tests job is there are no test results (#14884)

.circleci/config.yml

@@ -534,7 +534,14 @@ steps-tests: &steps-tests
           cd src
           export ELECTRON_OUT_DIR=Default
           (cd electron && npm run test -- --ci --enable-logging)
-
+    - run:
+        name: Check test results existence
+        command: |
+          MOCHA_FILE='src/junit/test-results.xml'
+          # Check if it exists and not empty.
+          if [ ! -s "$MOCHA_FILE" ]; then
+            exit 1
+          fi
     - store_test_results:
         path: src/junit