test: Check created_at for prepareData to ensure user order (#6436)

* test: Check created_at for prepareData to ensure user order

* test: Consistent user ordering in dbfake

* import order

* Linting

coderd/database/dbfake/databasefake.go

@@ -2922,6 +2922,21 @@ func (q *fakeQuerier) InsertUser(_ context.Context, arg database.InsertUserParam
 		return database.User{}, err
 	}
 
+	// There is a common bug when using dbfake that 2 inserted users have the
+	// same created_at time. This causes user order to not be deterministic,
+	// which breaks some unit tests.
+	// To fix this, we make sure that the created_at time is always greater
+	// than the last user's created_at time.
+	allUsers, _ := q.GetUsers(context.Background(), database.GetUsersParams{})
+	if len(allUsers) > 0 {
+		lastUser := allUsers[len(allUsers)-1]
+		if arg.CreatedAt.Before(lastUser.CreatedAt) ||
+			arg.CreatedAt.Equal(lastUser.CreatedAt) {
+			// 1 ms is a good enough buffer.
+			arg.CreatedAt = lastUser.CreatedAt.Add(time.Millisecond)
+		}
+	}
+
 	q.mutex.Lock()
 	defer q.mutex.Unlock()