diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix
index d3bd7746d89..d89bcfde481 100644
--- a/lib/tests/misc.nix
+++ b/lib/tests/misc.nix
@@ -236,6 +236,20 @@ runTests {
     };
   };
 
+  testOverrideExistingEmpty = {
+    expr = overrideExisting {} { a = 1; };
+    expected = {};
+  };
+
+  testOverrideExistingDisjoint = {
+    expr = overrideExisting { b = 2; } { a = 1; };
+    expected = { b = 2; };
+  };
+
+  testOverrideExistingOverride = {
+    expr = overrideExisting { a = 3; b = 2; } { a = 1; };
+    expected = { a = 1; b = 2; };
+  };
 
 # GENERATORS
 # these tests assume attributes are converted to lists