Modify the metrics test to set the prometheus_multiproc_dir environme…

…nt variable (#179)

test_api.py

@@ -6,6 +6,7 @@
 import test.support
 import uuid
 import copy
+import tempfile
 from app import create_app, db
 from app.auth.identity import Identity
 from app.utils import HostWrapper
@@ -1438,8 +1439,12 @@ def test_metrics(self):
         """
         The metrics endpoint simply returns 200 to any GET request.
         """
-        response = self.client().get(METRICS_URL)  # No identity header.
-        self.assertEqual(200, response.status_code)
+        with tempfile.TemporaryDirectory() as temp_dir:
+            with test.support.EnvironmentVarGuard() as env:
+                env.set("prometheus_multiproc_dir", temp_dir)
+
+                response = self.client().get(METRICS_URL)  # No identity header.
+                self.assertEqual(200, response.status_code)
 
     def test_version(self):
         response = self.get(VERSION_URL, 200)