test(coverage): set hpctixfile to a unique name

Sets hpctixfile to be unique for every postgrest process that
is run.

Previously, this was based on the test name, but issues arise
when two postgrest processes are run under the same test, which
generates two files where one gets overwritten by the other.

Consequently, coverage data used to get lost, which is now fixed
with this commit.

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>

test/io/config.py

@@ -4,6 +4,7 @@ import shutil
 import signal
 
 import pytest
+import uuid
 import yaml
 
 
@@ -80,10 +81,19 @@ def slow_schema_cache_env(defaultenv):
 
 
 def hpctixfile():
-    "Returns an individual filename for each test, if the HPCTIXFILE environment variable is set."
+    """
+    Returns a unique filename for each postgrest process that is
+    run, if the HPCTIXFILE environment variable is set.
+
+    Later, we combine these files using "hpc sum" to get the
+    complete coverage.
+    """
+
     if "HPCTIXFILE" not in os.environ:
         return ""
 
     tixfile = pathlib.Path(os.environ["HPCTIXFILE"])
-    test = hash(os.environ["PYTEST_CURRENT_TEST"])
+    # 12 chars are unique enough and chances of collisions are
+    # astronomically low.
+    test = uuid.uuid4().hex[:12]
     return tixfile.with_suffix(f".{test}.tix")