public async Task GetUsernameByOrderIdAsync_WithOrderId_ShouldReturnUsername()
{
// Arrange
FitStoreDbContext database = this.Database;
DatabaseHelper.SeedData(database);
IAdminUserService adminUserService = new AdminUserService(database);
// Act
string result = await adminUserService.GetUsernameByOrderIdAsync(orderId);
// Assert
result.Should().Be(firstUsername);
}