public async Task AssignRoleToUserAsync_RequestNull_ThrowArgumentNullException() { // Arrange UserRoleAssignmentRequest request = null; // Act + Assert ArgumentNullException exception = await Assert.ThrowsAsync <ArgumentNullException>(() => _identityService.AssignRoleToUserAsync(request)).ConfigureAwait(false); Assert.NotNull(exception); Assert.Equal(string.Format(ErrorMessages.NullExceptionMessage, "request"), exception.Message); }