AutoAssert

Free, MIT-licensed fluent assertions for .NET with familiar Should() syntax, deep object diffs, snapshot testing, and zero commercial license requirements.

Why AutoAssert instead of FluentAssertions?

• No commercial license requirement for commercial use.
• Familiar migration path: fluent Should() API for xUnit, NUnit, and MSTest.
• Deep diff output for BeEquivalentTo mismatches.
• AOT-safe direction with optional generated reflection-free equivalency comparers.

Install

dotnet add package Swevo.AutoAssert

Optional companion packages:

dotnet add package Swevo.AutoAssert.Analyzers
dotnet add package Swevo.AutoAssert.Generator
dotnet add package Swevo.AutoAssert.AspNetCore
dotnet add package Swevo.AutoAssert.Json

5-minute quickstart

using AutoAssert;

[Fact]
public void Order_total_is_calculated()
{
    var order = new { Subtotal = 100m, Tax = 20m, Total = 120m };

    order.Total.Should().Be(120m);
    order.Should().BeEquivalentTo(new { Subtotal = 100m, Tax = 20m, Total = 120m });
}

High-value examples

1) Basic assertions and fluent chaining

using AutoAssert;

"hello world".Should()
    .NotBeNullOrEmpty()
    .And.StartWith("hello")
    .And.EndWith("world");

5.Should().BePositive().And.BeLessThan(10);

2) Compare complex object graphs with full diffs

using AutoAssert;

var actual = new OrderDto
{
    Id = 42,
    Customer = new CustomerDto { Name = "Ada" },
    Lines = [new OrderLineDto { Sku = "ABC", Quantity = 2 }]
};

var expected = new
{
    Id = 42,
    Customer = new { Name = "Ada" },
    Lines = new[] { new { Sku = "ABC", Quantity = 2 } }
};

actual.Should().BeEquivalentTo(expected, options => options.WithStrictOrdering());

3) Aggregate failures with AssertionScope

using AutoAssert;

using (new AssertionScope())
{
    result.Name.Should().Be("Ada");
    result.Age.Should().Be(30);
    result.Email.Should().NotBeNullOrEmpty();
}

4) Snapshot tests with scrubbers

using AutoAssert;

result.Should().MatchSnapshot(
    scrub: SnapshotScrubbers.Combine(
        SnapshotScrubbers.Guids(),
        SnapshotScrubbers.IsoTimestamps()));

Migration comparison

AutoAssert is designed to keep common usage nearly identical:

Scenario	FluentAssertions style	AutoAssert style
Basic value	value.Should().Be(42);	value.Should().Be(42);
Null/empty	name.Should().NotBeNullOrEmpty();	name.Should().NotBeNullOrEmpty();
Exception	act.Should().Throw<InvalidOperationException>();	act.Should().Throw<InvalidOperationException>();
Equivalency	actual.Should().BeEquivalentTo(expected);	actual.Should().BeEquivalentTo(expected);

See deeper comparisons in docs/COMPARISON.md.

Recipes

Copy/paste recipes for common test scenarios:

• docs/RECIPES.md (collections, API payloads, async exceptions, snapshots)
• src/AutoAssert.AspNetCore/README.md (HTTP integration tests)
• src/AutoAssert.Json/README.md (raw JSON assertions)

Companion packages

Package	Purpose
Swevo.AutoAssert.Analyzers	Compile-time diagnostics for assertion footguns.
Swevo.AutoAssert.Generator	Reflection-free generated equivalency comparers.
Swevo.AutoAssert.AspNetCore	Fluent HttpResponseMessage assertions for integration tests.
Swevo.AutoAssert.Json	Fluent assertions over raw JSON strings.

Compatibility matrix

See docs/COMPATIBILITY.md for package-by-package target frameworks and test framework support.

Release notes

See CHANGELOG.md for version history and feature changes.

Growth and distribution assets

The repository now includes reusable go-to-market assets:

• docs/NUGET-LISTING.md for listing copy and metadata guidance.
• docs/DISTRIBUTION.md for release promotion checklist.
• docs/METRICS.md for a simple download and retention measurement model.

License

MIT © Justin Bannister