Improve test coverage reporting / accuracy (#7819)

* improve test coverage reporting / accuracy

* handle absolute coverpaths

* move tests into multiple files

* rename codecov.yml (https://github.com/codecov/support/issues/426)

codecov.yml

@@ -0,0 +1,8 @@
+coverage:
+  status:
+    project:
+      default:
+        threshold: 1%
+    patch: off
+ignore:
+  - store/storetest