C# – How to unit test code that uses Dapper

Dapper makes your code difficult to unit test. The problem is that Dapper uses static extension methods, and static methods are difficult to mock out. One approach is to wrap the Dapper static methods in a class, extract out an interface for that wrapper class, and then dependency inject the wrapper interface. In the unit … Read more C# – How to unit test code that uses Dapper

Algorithm Explained: Determine if two strings have a substring in common

Problem statement: Given two strings, determine if they have a substring in common. Example: Do “hello world” and “world” have a substring in common? Yes, they both have the substring “world”. Approach What are all the substrings of string? The string “word” is four characters long. It contains 10 substrings between length 1 and 4. … Read more Algorithm Explained: Determine if two strings have a substring in common

Python – Expect an exception using pytest

When you want to add a test to verify that an exception is raised, you can use pytest.raises() like this: When the code doesn’t raise an exception, you’ll see a test failed message like this: Example – Expect WordCounter to raise an exception I’m implementing the following WordCounter class using a test-driven approach. The first … Read more Python – Expect an exception using pytest

Refactoring the Nested Conditionals code smell

Nested conditionals are a code smell because they make the code harder to understand. They tend to grow more and more complicated over time because developers will keep adding conditions and more levels of nesting. The deeper the nesting, the more time it’ll eventually take to refactor it. Code Smell: Nested conditionals.Definition: A conditional block … Read more Refactoring the Nested Conditionals code smell

C# – Use StringAssert when testing a string for substrings

When you’re testing if two strings are equal, you can simply use Assert.AreEqual(). When you’re testing if a string contains a substring or a pattern, typically developers use Assert.IsTrue() with a substring method or regex. You should use StringAssert instead, because it gives better failure messages. The key problem is Assert.IsTrue() gives useless information. You … Read more C# – Use StringAssert when testing a string for substrings

C# – Default method implementations and constants in interfaces

Starting in C# 7, you can add default method implementations (and constants) to interfaces, like this: This outputs the following: Microsoft’s stated purpose for this feature is that it allows you add methods to an interface without breaking existing implementing classes. That’s nice, but it weakens the concept of interfaces (forcing implementers to adhere to … Read more C# – Default method implementations and constants in interfaces

Event-driven .NET: How to unit test code that depends on an event

Testing code with a dependency on an event can be tricky. You may be tempted to directly unit test the event handling method. However, that doesn’t prove that code under test is listening for the event. It’s better to really fire the event, and then test side effects of the event handling method. Firing the … Read more Event-driven .NET: How to unit test code that depends on an event

C# – Use DynamicData attribute to pass functions and objects into parameterized tests

The purpose of parameterized tests is to eliminate duplicated tests. There are two ways to pass parameters into a parameterized test: the DataRow attribute and the DynamicData attribute. With DataRow, the problem is you can only pass in constants and arrays. You can’t pass in reference types. When you try to pass in reference types, … Read more C# – Use DynamicData attribute to pass functions and objects into parameterized tests

Set Operations – Intersect, Union, Difference, and Symmetric Difference

In the show House, different sets of main characters appeared in different seasons. For example, here are the main characters that starred in seasons 1 and 7: Characters in Season 1 Characters in Season 7 HouseCuddyWilsonForemanChaseCameron HouseCuddyWilsonForemanChaseTaubThirteenMasters Set operations allow you to answer interesting questions, such as “Which House main characters appeared in both seasons … Read more Set Operations – Intersect, Union, Difference, and Symmetric Difference