python3Packages.buildPythonPackage: default enabledTestPaths = [ "." ]

Explicitly provide a default value for the argument `enabledTestPaths`
as the current working directory (`enabledTestPaths = [ "." ]`)
to simplify overriding (making `enabledTestPaths` always specified as a
non-empty list) while preserving `pytest`'s default behaviour of
discovering tests in the current working directory.

Assert the specified `enabledTestPaths` value to be a non-empty list.

pkgs/development/interpreters/python/mk-python-derivation.nix

@@ -431,6 +431,17 @@ let
       # Longer-term we should get rid of `checkPhase` and use `installCheckPhase`.
       installCheckPhase = attrs.checkPhase;
     }
+    // {
+      # `pytest` defaults to discover tests in the current directory if no paths or test items are specified.
+      # Provide an explicit default value to simplify overriding.
+      enabledTestPaths =
+        if attrs ? enabledTestPaths then
+          lib.throwIf (!lib.isList attrs.enabledTestPaths || attrs.enabledTestPaths == [ ])
+            "${lib.getName finalAttrs}: enabledTestPaths must be a non-empty list (default to [ \".\" ])."
+            attrs.enabledTestPaths
+        else
+          [ "." ];
+    }
     //
       lib.mapAttrs
         (
@@ -442,7 +453,6 @@ let
         (
           getOptionalAttrs [
             "enabledTestMarks"
-            "enabledTestPaths"
             "enabledTests"
           ] attrs
         )