Moq – Verifying parameters passed to a mocked method

When you need to verify that the code under test called a method with the expected parameters, you can mock the method with Moq and use Verify() + It.Is<T>() to check the parameters passed in. Verify() asserts that the method call happened as expected with the specified parameters. Here’s an example. This is verifying that … Read more

Moq – How to use Callback() to capture parameters passed to mocked methods

When you’re using Moq to set up a mocked method, you can use Callback() to capture the parameters passed into the mocked method: There are two main use cases for capturing parameters in a test: Logging method calls for troubleshooting. Simplifying assertions involving complex parameters. In this article, I’ll show examples of using Callback() in … Read more

Error CS0854 when you’re using Moq with optional parameters

Problem Optional parameters aren’t optional when you’re using Moq. When you’re setting up or verifying a method call on a mock object, and the method has an optional parameter that you didn’t specify a value for, you’ll get the following compiler error: Error CS0854 – An expression tree may not contain a call or invocation … Read more

Algorithm Explained: Get the max items you can purchase with a fixed budget

Problem statement: Given a fixed budget and a list of item prices. What is the max number of items you can purchase? You can only buy each item once. Note: This is the Mark and Toys problem from HackerRank. Example: You’re given $10 and a list of items to choose from: A cool coffee cup … Read more

C# – Search XML for elements, values, and attributes

The simplest way to search XML is to use the Linq-to-XML API in .NET (in System.Xml.Linq). This parses XML and allows you to perform Linq queries on it. Here’s an example: This outputs: XElement is the main class. You use it in combination with Linq methods to perform searches. In this article, I’ll how to … Read more

C# – Circuit breaker with Polly

In an electrical system, a circuit breaker detects electrical problems and opens the circuit, which blocks electricity from flowing. To get electricity flowing again, you have to close the circuit. The same approach can be implemented in software when you’re sending requests to an external service. This is especially important when you’re sending lots of … Read more

C# – How to update appsettings.json programmatically

You have to overwrite the appsettings.json file to be able to update values programmatically. You have to deal with the whole file, not individual parts of it. The process can be summarized in the following steps: Load appsettings.json and deserialize it into an object. Update properties on the object. Serialize the object into a JSON … Read more

C# – Global exception event handlers

There are two global exception event available in all .NET applications: FirstChanceException: When any exception is thrown, this event is fired before anything else. UnhandledException: When there’s an unhandled exception, this event is fired right before the process is terminated. You wire up these event handlers in Main() (before anything else has executed), like this: … Read more

C# – How to load assemblies at runtime using Microsoft Extensibility Framework (MEF)

You can use Microsoft Extensibility Framework (MEF) to load assemblies at runtime. This is an alternative to implementing dynamic assembly loading with a more manual approach (like using AssemblyLoadContext). Here’s an example of using MEF to load an instance of IMessageProcessorPlugin from some assembly located in the C:\Plugins directory: MEF looks for exported types in … Read more

C# – Check if a string contains any substring from a list

There are many different scenarios where you might want to check a string against a list of substrings. Perhaps you’re dealing with messy exception handling and have to compare the exception message against a list of known error messages to determine if the error is transient or not. When you need to check a string … Read more