fix: use parallel relation fetching (#173)

optimizes performance of queries with many left joins

packages/medusa-test-utils/src/mock-repository.js

@@ -6,6 +6,7 @@ class MockRepo {
     softRemove,
     find,
     findOne,
+    findOneWithRelations,
     findOneOrFail,
     save,
     findAndCount,
@@ -19,6 +20,7 @@ class MockRepo {
     this.findOneOrFail_ = findOneOrFail;
     this.save_ = save;
     this.findAndCount_ = findAndCount;
+    this.findOneWithRelations_ = findOneWithRelations;
   }
 
   setFindOne(fn) {
@@ -53,6 +55,11 @@ class MockRepo {
       return this.findOneOrFail_(...args);
     }
   });
+  findOneWithRelations = jest.fn().mockImplementation((...args) => {
+    if (this.findOneWithRelations_) {
+      return this.findOneWithRelations_(...args);
+    }
+  });
   findOne = jest.fn().mockImplementation((...args) => {
     if (this.findOne_) {
       return this.findOne_(...args);