fix: Fix broken tp/cg filtering/update in testplan.py

src/dvsim/testplan.py

@@ -560,6 +560,19 @@ def _parse_testplan(self, filename: Path, tags: set[str], repo_top: Path) -> Non
         Testplan._check_duplicates("testpoint", all_tps)
         Testplan._check_duplicates("covergroup", all_cgs)
 
+        # The testplan might have been filtered with a set of tags. Apply that
+        # filter, then check that we haven't discarded everything.
+        self.testpoints = [t for t in all_tps if t.has_tags(tags)]
+        self.covergroups = [cg for cg in all_cgs if cg.has_tags(tags)]
+
+        if not (self.testpoints or self.covergroups):
+            msg = (
+                f"Merged testplan has no testpoints or covergroups, after "
+                f"filtering with tags {tags}. Before filtering, the numbers of "
+                f"testpoints and covergroups were {len(all_tps)}, {len(all_cgs)}."
+            )
+            raise ValueError(msg)
+
         # Wildcards in testpoints can mostly point to any value from the
         # object. The following names are *not* allowed (because they wouldn't
         # really make much sense).