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Boolean Assertions

TUnit provides simple, expressive assertions for testing boolean values. These assertions work with both bool and bool? (nullable boolean) types.

Basic Boolean Assertions​

IsTrue​

Tests that a boolean value is true:

[Test]
public async Task Value_Is_True()
{
    var isValid = ValidateInput("test@example.com");
    await Assert.That(isValid).IsTrue();

    var hasPermission = user.HasPermission("write");
    await Assert.That(hasPermission).IsTrue();
}

IsFalse​

Tests that a boolean value is false:

[Test]
public async Task Value_Is_False()
{
    var isExpired = CheckIfExpired(futureDate);
    await Assert.That(isExpired).IsFalse();

    var isEmpty = list.Length == 0;
    await Assert.That(isEmpty).IsFalse();
}

Alternative: Using IsEqualTo​

You can also use IsEqualTo() for boolean comparisons:

[Test]
public async Task Using_IsEqualTo()
{
    var result = PerformCheck();

    await Assert.That(result).IsEqualTo(true);
    // Same as: await Assert.That(result).IsTrue();

    await Assert.That(result).IsEqualTo(false);
    // Same as: await Assert.That(result).IsFalse();
}

However, IsTrue() and IsFalse() are more expressive and recommended for boolean values.

Nullable Booleans​

Both assertions work with nullable booleans (bool?):

[Test]
public async Task Nullable_Boolean_True()
{
    bool? result = GetOptionalFlag();

    await Assert.That(result).IsTrue();
    // This asserts both:
    // 1. result is not null
    // 2. result.Value is true
}

[Test]
public async Task Nullable_Boolean_False()
{
    bool? result = GetOptionalFlag();

    await Assert.That(result).IsFalse();
    // This asserts both:
    // 1. result is not null
    // 2. result.Value is false
}

Null Nullable Booleans​

If a nullable boolean is null, both IsTrue() and IsFalse() will fail:

[Test]
public async Task Nullable_Boolean_Null()
{
    bool? result = null;

    // These will both fail:
    // await Assert.That(result).IsTrue();  // ❌ Fails - null is not true
    // await Assert.That(result).IsFalse(); // ❌ Fails - null is not false

    // Check for null first:
    await Assert.That(result).IsNull();
}

Chaining Boolean Assertions​

Boolean assertions can be chained with other assertions:

[Test]
public async Task Chained_With_Other_Assertions()
{
    bool? flag = GetFlag();

    await Assert.That(flag)
        .IsNotNull()
        .And.IsTrue();
}

Practical Examples​

Validation Results​

[Test]
public async Task Email_Validation()
{
    var isValid = ValidateEmail("test@example.com");
    await Assert.That(isValid).IsTrue();

    var isInvalid = ValidateEmail("not-an-email");
    await Assert.That(isInvalid).IsFalse();
}

Permission Checks​

[Test]
public async Task User_Permissions()
{
    var user = await GetUserAsync("alice");

    await Assert.That(user.CanRead).IsTrue();
    await Assert.That(user.CanWrite).IsTrue();
    await Assert.That(user.CanDelete).IsFalse();
}

State Flags​

[Test]
public async Task Service_State()
{
    var service = new ExampleBackgroundService();

    await Assert.That(service.IsRunning).IsFalse();

    await service.StartAsync();

    await Assert.That(service.IsRunning).IsTrue();
}

Feature Flags​

[Test]
public async Task Feature_Toggles()
{
    var config = LoadConfiguration();

    await Assert.That(config.EnableNewFeature).IsTrue();
    await Assert.That(config.EnableBetaFeature).IsFalse();
}

Tip: Prefer Specific Assertions​

When testing the boolean result of a comparison, use the specific assertion instead for clearer failure messages:

[Test]
public async Task Prefer_Specific_Assertions()
{
    var count = GetCount();

    // Less clear — failure message says "expected true but was false":
    await Assert.That(count > 0).IsTrue();

    // More clear — failure message shows the actual value:
    await Assert.That(count).IsGreaterThan(0);
}

Use IsTrue() / IsFalse() for actual boolean values and flags. For comparisons, collections, strings, and types, TUnit provides dedicated assertions with better failure messages.

See Also​