fix: Allow skipping useExisting. (#1070)

Fixes #1066

packages/orm/src/newTestInstance.ts

@@ -42,6 +42,7 @@ import { assertNever, maybeRequireTemporal } from "./utils";
 export type FactoryOpts<T extends Entity> = DeepPartialOpts<T> & {
   use?: Entity | Entity[];
   useFactoryDefaults?: boolean | "none";
+  useExistingCheck?: boolean;
 };
 
 // Chosen b/c it's a monday https://www.timeanddate.com/calendar/monthly.html?year=2018&month=1&country=1
@@ -168,7 +169,7 @@ export function newTestInstance<T extends Entity>(
 
   const createOpts = Object.fromEntries(initialOpts);
 
-  if (factoryOpts.useExisting) {
+  if (factoryOpts.useExisting && testOpts.useExistingCheck !== false) {
     const existing = em.entities
       .filter((e) => e instanceof meta.cstr)
       .find((e) => factoryOpts.useExisting!(createOpts as OptsOf<T>, e as DeepNew<T>));

packages/tests/integration/src/EntityManager.factories.test.ts

@@ -398,6 +398,22 @@ describe("EntityManager.factories", () => {
     expect(a2).toMatchEntity(a1);
   });
 
+  it("can skip creating a singleton", async () => {
+    const em = newEntityManager();
+    // Given we have an existing author
+    const a1 = newTestInstance(em, Author, {}, {});
+    // And a factory wants to dedup authors on firstName
+    const a2 = newTestInstance(
+      em,
+      Author,
+      // But the test wants to skip it
+      { useExistingCheck: false },
+      { useExisting: (opts, existing) => opts.firstName === existing.firstName },
+    );
+    // Then we got back a new author
+    expect(a2).not.toMatchEntity(a1);
+  });
+
   it("can create and leave required fields unset with noValue", async () => {
     const em = newEntityManager();
     // Given we want to make a Book