gating: run bundled tests instead of just import

plan.fmf

@@ -6,8 +6,12 @@ environment:
 
 discover:
   how: shell
+  dist-git-source: true
   tests:
-  - name: import_test
-    test: "python${pybasever} -c 'import ply'"
+  - name: bundled tests
+    test: |
+      cd $TMT_SOURCE_DIR/ply-*/test &&
+      python${pybasever} testyacc.py &&
+      python${pybasever} testlex.py
     require:
-    - "python${pybasever}-ply"
+    - python${pybasever}-ply