Testing Your Code When Using Polly

Mar 10, 2019 # Polly, Testing, Unit Test

Full source code here.

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When developing an application with Polly you will also probably want to write some unit tests.

Here are the scenarios I test for -

How my code behaves when the policy throws an exception, such as TimeoutRejectionException, BulkheadRejectedException or BrokenCircuitException.
How my code behaves when a policy becomes active and changes the outcome of a call, such as when an unreliable request works because Polly performs a retry.
What my code should do if there was no policy in place.

I have a few classes to demonstrate these scenarios, BusinessLogic.cs and OtherBusinessLogic.cs are the classes under test. ErrorProneCode.cs is the unreliable class that I will mock and pass mocked policies into.

For the first case I use Moq to mock the error prone code so it returns an incorrect value.

 1[Fact]
 2public void Should_Return_999_When_TimeoutRejectedException_Thrown()
 3{
 4    //Arrange 
 5    Mock<IErrorProneCode> mockedErrorProneCode = new Mock<IErrorProneCode>();
 6    mockedErrorProneCode.Setup(e => e.GetSomeNumber()).Returns(0);
 7
 8    Mock<ISyncPolicy> mockedPolicy = new Mock<ISyncPolicy>();
 9    mockedPolicy.Setup(p => p.Execute(It.IsAny<Func<int>>())).Throws(new TimeoutRejectedException("Mocked Timeout Exception"));
10
11    IBusinessLogic businessLogic = new BusinessLogic(mockedPolicy.Object, mockedErrorProneCode.Object);
12
13    //Act
14    // if there is a TimeoutRejectedException in this CallSomeSlowBadCode it will return 999
15    int num = businessLogic.CallSomeSlowBadCode();
16
17    //Assert
18    Assert.Equal(999, num);
19}

In the next case I verify that the application has correctly used the retry policy method. I use a seeded random number generator that produces an known sequence to return values from the ErrorProneCode class.

 1[Fact]
 2public void Should_Return_Odd_When_Retry()
 3{
 4    //Arrange 
 5    Mock<IErrorProneCode> mockedErrorProneCode = new Mock<IErrorProneCode>();
 6
 7    Random rnd = new Random(1); // rnd.Next(10) retruns 2, 1, 4 
 8
 9    mockedErrorProneCode.Setup(e => e.GetSomeNumber()).Returns(() => rnd.Next(10));
10
11    ISyncPolicy<int> policy = Policy.HandleResult<int>(i => i %2 !=1) // retry if the number is not odd.
12        .Retry(1);
13    OtherBusinessLogic otherBusinessLogic = new OtherBusinessLogic(policy, mockedErrorProneCode.Object);
14
15    //Act
16    int num = otherBusinessLogic.CallSomeCodeThatNeedsToBeRetried();
17
18    //Assert
19    Assert.Equal(1, num % 2);
20}

Finally, I want to verify that my code will work if no Polly policy is in use. To do this, I pass in a NoOp policy.

 1[Fact]
 2public void Should_Return_Even_With_NoOp()
 3{
 4    //Arrange 
 5    Mock<IErrorProneCode> mockedErrorProneCode = new Mock<IErrorProneCode>();
 6
 7    Random rnd = new Random(1); // rnd.Next(10) retruns 2, 1, 4 
 8
 9    mockedErrorProneCode.Setup(e => e.GetSomeNumber()).Returns(() => rnd.Next(10));
10
11    ISyncPolicy<int> policy = Policy.NoOp<int>();
12    OtherBusinessLogic otherBusinessLogic = new OtherBusinessLogic(policy, mockedErrorProneCode.Object);
13
14    //Act
15    int num = otherBusinessLogic.CallSomeCodeThatNeedsToBeRetried();
16
17    //Assert
18    Assert.Equal(0, num % 2); //even number
19}

Full source code here.

Polly Testing Unit Test

Testing Your Code When Using Polly

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