𝗕𝗲𝘀𝘁 𝗣𝗿𝗮𝗰𝘁𝗶𝗰𝗲𝘀 𝗳𝗼𝗿 𝗪𝗿𝗶𝘁𝗶𝗻𝗴 𝗨𝗻𝗶𝘁 𝗧𝗲𝘀𝘁𝘀 𝗶𝗻 .𝗡𝗘𝗧 𝘄𝗶𝘁𝗵 𝘅𝗨𝗻𝗶𝘁

Unit testing is essential for building reliable and maintainable .NET applications. Whether you're just getting started with 𝘅𝗨𝗻𝗶𝘁 or want to sharpen your test-writing approach, here are 𝟭𝟬 𝗯𝗲𝘀𝘁 𝗽𝗿𝗮𝗰𝘁𝗶𝗰𝗲𝘀 every .NET developer should follow.

✅ 𝟭. 𝗔𝘃𝗼𝗶𝗱 𝗜𝗻𝗳𝗿𝗮𝘀𝘁𝗿𝘂𝗰𝘁𝘂𝗿𝗲 𝗗𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝗰𝗶𝗲𝘀

• Tests should be fast and isolated.
• Use Dependency Injection.
• Separate unit tests from integration tests in different projects.

✅ 𝟮. 𝗙𝗼𝗹𝗹𝗼𝘄 𝗧𝗲𝘀𝘁 𝗡𝗮𝗺𝗶𝗻𝗴 𝗦𝘁𝗮𝗻𝗱𝗮𝗿𝗱𝘀
Structure test names as:
MethodName_Scenario_ExpectedBehavior()

𝗘𝘅𝗮𝗺𝗽𝗹𝗲:

[Fact]
public void Add_SingleNumber_ReturnsSameNumber()

✅ 𝟯. 𝗨𝘀𝗲 𝗔𝗿𝗿𝗮𝗻𝗴𝗲, 𝗔𝗰𝘁, 𝗔𝘀𝘀𝗲𝗿𝘁 (𝗔𝗔𝗔)
Make your tests easier to read and maintain.

𝗘𝘅𝗮𝗺𝗽𝗹𝗲:

[Fact]
public void Add_EmptyString_ReturnsZero()
{
var calculator = new StringCalculator(); // Arrange
var result = calculator.Add(""); // Act
Assert.Equal(0, result); // Assert
}

✅ 𝟰. 𝗪𝗿𝗶𝘁𝗲 𝗠𝗶𝗻𝗶𝗺𝗮𝗹𝗹𝘆 𝗣𝗮𝘀𝘀𝗶𝗻𝗴 𝗧𝗲𝘀𝘁𝘀
Use the simplest inputs necessary to validate the behavior.

𝗣𝗿𝗲𝗳𝗲𝗿:

calculator.Add("0");

𝗢𝘃𝗲𝗿:

calculator.Add("42");

✅ 𝟱. 𝗔𝘃𝗼𝗶𝗱 𝗠𝗮𝗴𝗶𝗰 𝗦𝘁𝗿𝗶𝗻𝗴𝘀
Use well-named constants for readability and clarity.

𝗜𝗻𝘀𝘁𝗲𝗮𝗱 𝗼𝗳:

calculator.Add("1001");

𝗨𝘀𝗲:

const string MAX_INPUT = "1001";
calculator.Add(MAX_INPUT);

✅ 𝟲. 𝗔𝘃𝗼𝗶𝗱 𝗟𝗼𝗴𝗶𝗰 𝗶𝗻 𝗧𝗲𝘀𝘁𝘀
No loops, conditionals, or switch statements.

𝗣𝗿𝗲𝗳𝗲𝗿:

[Theory]
[InlineData("1,2,3", 6)]
[InlineData("4,5", 9)]

𝗢𝘃𝗲𝗿:

foreach (var test in testCases) { ... }

✅ 𝟳. 𝗨𝘀𝗲 𝗛𝗲𝗹𝗽𝗲𝗿 𝗠𝗲𝘁𝗵𝗼𝗱𝘀 𝗜𝗻𝘀𝘁𝗲𝗮𝗱 𝗼𝗳 𝗦𝗲𝘁𝘂𝗽/𝗧𝗲𝗮𝗿𝗗𝗼𝘄𝗻
xUnit doesn’t use [SetUp] and [TearDown].
Use constructors or private methods.

𝗘𝘅𝗮𝗺𝗽𝗹𝗲:

private StringCalculator CreateDefaultStringCalculator()
{
return new StringCalculator();
}

✅ 𝟴. 𝗔𝘃𝗼𝗶𝗱 𝗠𝘂𝗹𝘁𝗶𝗽𝗹𝗲 𝗔𝗰𝘁 𝗦𝘁𝗲𝗽𝘀
Each test should validate a single action only.

𝗜𝗻𝘀𝘁𝗲𝗮𝗱 𝗼𝗳:

var result1 = calculator.Add("");
var result2 = calculator.Add(",");

𝗦𝗽𝗹𝗶𝘁 𝗶𝗻𝘁𝗼 𝘀𝗲𝗽𝗮𝗿𝗮𝘁𝗲 𝘁𝗲𝘀𝘁 𝗰𝗮𝘀𝗲𝘀 𝗼𝗿 𝘂𝘀𝗲:

[Theory]
[InlineData("", 0)]
[InlineData(",", 0)]

✅ 𝟵. 𝗧𝗲𝘀𝘁 𝗣𝗿𝗶𝘃𝗮𝘁𝗲 𝗠𝗲𝘁𝗵𝗼𝗱𝘀 𝘃𝗶𝗮 𝗣𝘂𝗯𝗹𝗶𝗰 𝗠𝗲𝘁𝗵𝗼𝗱𝘀
Avoid direct testing of private methods.
Test them through public behavior.

𝗘𝘅𝗮𝗺𝗽𝗹𝗲:

Assert.Equal("a", parser.ParseLogLine(" a "));

✅ 𝟭𝟬. 𝗛𝗮𝗻𝗱𝗹𝗲 𝗦𝘁𝗮𝘁𝗶𝗰 𝗗𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝗰𝗶𝗲𝘀 𝗖𝗮𝗿𝗲𝗳𝘂𝗹𝗹𝘆
Wrap static calls in abstractions and inject them so you can mock them during testing.

𝗪𝗵𝗶𝗰𝗵 𝗼𝗳 𝘁𝗵𝗲𝘀𝗲 𝗽𝗿𝗮𝗰𝘁𝗶𝗰𝗲𝘀 𝗵𝗮𝘀 𝗺𝗮𝗱𝗲 𝘁𝗵𝗲 𝗯𝗶𝗴𝗴𝗲𝘀𝘁 𝗱𝗶𝗳𝗳𝗲𝗿𝗲𝗻𝗰𝗲 𝗶𝗻 𝘆𝗼𝘂𝗿 𝘁𝗲𝘀𝘁𝗶𝗻𝗴 𝗮𝗽𝗽𝗿𝗼𝗮𝗰𝗵?
𝗗𝗼 𝘆𝗼𝘂 𝗳𝗼𝗹𝗹𝗼𝘄 𝗮𝗻𝘆 𝗼𝘁𝗵𝗲𝗿 𝘅𝗨𝗻𝗶𝘁 𝗼𝗿 𝘁𝗲𝘀𝘁𝗶𝗻𝗴 𝘀𝘁𝗿𝗮𝘁𝗲𝗴𝗶𝗲𝘀 𝘁𝗵𝗮𝘁 𝘆𝗼𝘂 𝘀𝘄𝗲𝗮𝗿 𝗯𝘆?