xUnit2032 v2 v3 Info

Type assertions based on 'assignable from' are confusingly named

Cause

A violation of this rule occurs when using Assert.IsAssignableFrom (or Assert.IsNotAssignableFrom).

Reason for rule

There is confusing about which arguments is “from” and when is “to” when using Assert.IsAssignableFrom (and Assert.IsNotAssignableFrom). We have added an overload of Assert.IsType (and Assert.IsNotType) that allows users to pass a flag whether they want strict (“exact”) type matching behavior (like Assert.IsType without the flag) or compatible (“inexact”) type matching behavior (like Assert.IsAssignableFrom).

How to fix violations

To fix a violation of this rule, convert the assertion to Assert.IsType (or Assert.IsNotType) using exactMatch: false.

Examples

Violates

using Xunit;

public class xUnit2032
{
    [Fact]
    public void TestMethod()
    {
        Assert.IsAssignableFrom<object>("Hello world");
    }
}

using Xunit;

public class xUnit2032
{
    [Fact]
    public void TestMethod()
    {
        Assert.IsNotAssignableFrom<object>("Hello world");
    }
}

Does not violate

using Xunit;

public class xUnit2032
{
    [Fact]
    public void TestMethod()
    {
        Assert.IsType<object>("Hello world", exactMatch: false);
    }
}

using Xunit;

public class xUnit2032
{
    [Fact]
    public void TestMethod()
    {
        Assert.IsNotType<object>("Hello world", exactMatch: false);
    }
}