feat(core): adjust the coverage file output for multicore tests

When the tests are run using multiple cores, there will

be one .coverage file for each core. So that the one file

is not being overwritten many times, using unique

filename for each core.

[no changelog]

core/prof/prof.py

@@ -50,7 +50,14 @@ class _Prof:
 
     def write_data(self):
         print("Total traces executed: ", __prof__.trace_count)
-        with open(".coverage", "w") as f:
+        # In case of multithreaded tests, we might be called multiple times.
+        # Making sure the threads do not overwrite each other's data.
+        worker_id = getenv("PYTEST_XDIST_WORKER")
+        if worker_id:
+            file_name = f".coverage.{worker_id}"
+        else:
+            file_name = ".coverage"
+        with open(file_name, "w") as f:
             # wtf so private much beautiful wow
             f.write("!coverage.py: This is a private format, don't read it directly!")
             # poormans json
@@ -67,10 +74,13 @@ class AllocCounter:
         if self.last_line is None:
             return
 
-        entry = self.data.setdefault(self.last_line, {
-            "total_allocs": 0,
-            "calls": 0,
-        })
+        entry = self.data.setdefault(
+            self.last_line,
+            {
+                "total_allocs": 0,
+                "calls": 0,
+            },
+        )
         entry["total_allocs"] += allocs
         entry["calls"] += 1