perf: only clone schema once in addMocksToSchema (#6201)

* perf: only clone schema once in `addMocksToSchema`

* chore: add changeset

.changeset/four-items-live.md

@@ -0,0 +1,5 @@
+---
+'@graphql-tools/mock': patch
+---
+
+perf: only clone schema once in `addMocksToSchema`

packages/mock/src/addMocksToSchema.ts

@@ -249,6 +249,8 @@ export function addMocksToSchema<TResolvers = IResolvers>({
     ? addResolversToSchema({
         schema: schemaWithMocks,
         resolvers: resolvers as any,
+        // This option ensures that schemas are not cloned multiple times, which can be very expensive
+        updateResolversInPlace: true,
       })
     : schemaWithMocks;
 }

packages/mock/tests/addMocksToSchema.spec.ts

@@ -388,4 +388,25 @@ describe('addMocksToSchema', () => {
 
     expect(viewer.name).toEqual('custom mock for String');
   });
+
+  it('creates a new schema whether or not resolvers are passed in', () => {
+    expect(
+      Object.is(
+        addMocksToSchema({
+          schema,
+          resolvers: {},
+        }),
+        schema,
+      ),
+    ).toBe(false);
+
+    expect(
+      Object.is(
+        addMocksToSchema({
+          schema,
+        }),
+        schema,
+      ),
+    ).toBe(false);
+  });
 });