How to unit test azure function using Xunit and Moq - asp.net-core

Question

I am very new to unit tests and recently started learning it from various online resources.
But still it confuses me when I need to implement it in my code.
For the given image which I have attached here, could anyone of you suggest me how should I start or where to start?
This is Azure function which I will be creating unit test for, framework/library I would prefer is Xunit and moq.

Answer 1

As mentioned in a comment, a good place to start when unit testing is looking at your code and identifying the different "paths" it can take and what the result of that path will be.
if (inventoryRequest != null)
{
// path 1
await _inventoryService.ProcessRequest(inventoryRequest);
_logger.LogInformation("HBSI Inventory Queue trigger function processed.");
}
else
{
// path 2
_logger.LogInformation("Unable to process HBSI Rate plan Queue.");
}
In your code, because of your if statement, there are 2 possible paths which will end in 2 different results = 2 unit tests.
Now you can start creating your unit tests but first you need to find out what you need to set up to be able to trigger your code.
private readonly ILogger _logger;
private readonly IInventoryService _inventoryService;
public InventoryServiceBusFunction(ILogger logger, IInventoryService inventoryService)
{
_logger = logger;
_inventoryService = inventoryService;
}
You have some dependencies being passed into your constructor with interfaces - great, this means we can mock them. We want to mock dependencies in unit tests because we want to control their behaviour for the tests. Also, mocking the dependencies negates any "real" behaviour the dependency might be performing i.e. database operations, API calls etc.
Using Moq we can mock the objects like so:
public class InventoryServiceBusFunctionTests
{
private readonly Mock<ILogger> _mockLogger = new Mock<ILogger>();
private readonly Mock<IInventoryService> _mockInventoryService = new Mock<IInventoryService>();
...
We will use these mocks later to make verifications on behaviour we expect to happen.
Next, we need to create an instance of the actual class we want to test.
// using a constructor in the test class will run this code before each test
public InventoryServiceBusFunctionTests()
{
// pass the mocked objects to initialize class
_inventoryServiceBusFunction = new InventoryServiceBusFunction(_mockLogger.Object, _mockInventoryService.Object);
}
Now that we have an instance of the InventoryServiceBusFunction class, we can use any of the public properties/methods in our tests.
[Fact]
public async Task GivenInventoryRequest_WhenFunctionRuns_ThenInventoryServiceProcessesRequest()
{
Now, remembering the paths from earlier, we can start to create the test cases. We can take the first path and create a [Fact] for it. You want to give your test case a meaningful name. I usually use the style of Given_When_Then to describe what is expected to happen.
Next, I usually add 3 comment sections to my test case:
// arrange
// act
// assert
This allows me to clearly see which parts of the test are doing what.
// act
await _inventoryServiceBusFunction.Run(inventoryRequest);
Next, I would fill in the \\ act section because this will tell me (via Intellisense) what I need to arrange. e.g. above, when hovering my mouse over the Run method, I can see that I need to pass an instance of InventoryRequest.
// arrange
var inventoryRequest = new InventoryRequest
{
Name = "abc123",
Quantity = 2,
Tags = new List<string>
{
"foo"
}
};
In the \\ arrange section, initialize an instance of the InventoryRequest class and set the properties. This can be any data as we aren't really interested in the data itself but more what happens when the code runs.
if (inventoryRequest != null)
{
// path 1
await _inventoryService.ProcessRequest(inventoryRequest);
_logger.LogInformation("HBSI Inventory Queue trigger function processed.");
}
Lastly, the \\ assert section. Here, we want to make assertions on what we expect to happen given the set up of the test. So given the InventoryRequest is not null, we expect the if to evaluate to true and we expect the _inventoryService.ProcessRequest(inventoryRequest) method to be executed.
// assert
_mockInventoryService
.Verify(x => x.ProcessRequest(It.Is<InventoryRequest>(ir => ir.Name == inventoryRequest.Name
&& ir.Quantity == inventoryRequest.Quantity
&& ir.Tags.Contains(inventoryRequest.Tags[0]))));
In Moq, we can use the .Verify() method on the mock object to assert that the method was called. We can use the It.Is<T> syntax to make assertions on the data that is passed to the method.
Here is the full test case for path 1:
[Fact]
public async Task GivenInventoryRequest_WhenFunctionRuns_ThenInventoryServiceProcessesRequest()
{
// arrange
var inventoryRequest = new InventoryRequest
{
Name = "abc123",
Quantity = 2,
Tags = new List<string>
{
"foo"
}
};
// act
await _inventoryServiceBusFunction.Run(inventoryRequest);
// assert
_mockInventoryService
.Verify(x => x.ProcessRequest(It.Is<InventoryRequest>(ir => ir.Name == inventoryRequest.Name
&& ir.Quantity == inventoryRequest.Quantity
&& ir.Tags.Contains(inventoryRequest.Tags[0]))));
}
Then for path 2, you are setting up the test so that the else condition is executed.
[Fact]
public async Task GivenInventoryRequestIsNull_WhenFunctionRuns_ThenInventoryServiceDoesNotProcessRequest()
{
// arrange
InventoryRequest inventoryRequest = null;
// act
await _inventoryServiceBusFunction.Run(inventoryRequest);
// assert
_mockInventoryService
.Verify(x => x.ProcessRequest(It.IsAny<InventoryRequest>()), Times.Never);
}
Note - in the \\ assert here, I am asserting that the await _inventoryService.ProcessRequest(inventoryRequest) method is never called. This is because you want the test to fail in this scenario as the method should only be executed in the if condition. You may also choose to verify that the logger method is called with the correct message.