CtrlK
BlogDocsLog inGet started
Tessl Logo

testland/fluentassertions

Reference for FluentAssertions - the canonical .NET fluent-assertion library pairable with xUnit / NUnit / MSTest; provides `.Should()` extension API (`.Should().Be()`, `.Should().BeOfType()`, `.Should().Throw()`, `.Should().BeEquivalentTo()` for deep equality, `.Should().Satisfy()` for predicates, `.Should().BeApproximately()` for floats); rich failure messages with object structure visualization. Covers the v8 license change: v8+ is free for open-source and non-commercial use but requires a paid license for commercial use, while v7 remains fully open-source. Use when a .NET test project needs deep object comparison or better failure output than `Assert.X` gives, when assertions must survive a move between xUnit / NUnit / MSTest, or when picking between v7 and v8+ on license grounds.

76

Quality

95%

Does it follow best practices?

Run evals on this skill

Adds up to 20 points to the overall score

View guide

SecuritybySnyk

Passed

No findings from the security scan

Overview
Quality
Evals
Security
Files

matchers.mdreferences/

FluentAssertions matcher catalog

Complete .Should() matcher reference. Core examples live in SKILL.md Step 3; this file is the full catalog. Per fluentassertions.com/introduction.

Equality

value.Should().Be(expected);
value.Should().NotBe(expected);
value.Should().BeNull();
value.Should().NotBeNull();
value.Should().BeSameAs(other);     // reference equality

Numeric

n.Should().BeGreaterThan(0);
n.Should().BeLessThanOrEqualTo(100);
d.Should().BeApproximately(3.14, 0.01);

String

s.Should().StartWith("prefix");
s.Should().EndWith("suffix");
s.Should().Contain("substring");
s.Should().Match("*wildcard*");
s.Should().MatchRegex(@"\d+");
s.Should().NotBeNullOrEmpty();

Collections

list.Should().HaveCount(3);
list.Should().Contain("alice");
list.Should().NotContain("eve");
list.Should().ContainInOrder("alice", "bob");
list.Should().BeEquivalentTo(other);   // any order
list.Should().AllSatisfy(x => x.Should().BePositive());

Type checks

result.Should().BeOfType<Success>();
result.Should().BeAssignableTo<IResult>();

Exceptions

Action act = () => DoSomething();
act.Should().Throw<ArgumentException>()
   .WithMessage("*invalid*")
   .Where(e => e.ParamName == "name");

// Async
Func<Task> asyncAct = async () => await DoSomethingAsync();
await asyncAct.Should().ThrowAsync<HttpRequestException>();

// Should NOT throw
act.Should().NotThrow();

Boolean + null

flag.Should().BeTrue();
flag.Should().BeFalse();
opt.Should().BeNull();
opt.Should().NotBeNull().And.NotBeEmpty();

Custom predicates

user.Should().Satisfy(u => u.Email.Contains("@") && u.Age >= 18);

BeEquivalentTo deep equality

Structural comparison; the most powerful matcher.

var actual = new User { Id = 1, Name = "Alice", Address = new Address { City = "NYC" } };
var expected = new User { Id = 1, Name = "Alice", Address = new Address { City = "NYC" } };
actual.Should().BeEquivalentTo(expected);   // passes (deep equal)

// Across different types (record vs class):
var dto = new UserDto { Id = 1, Name = "Alice" };
user.Should().BeEquivalentTo(dto, opts => opts
    .Excluding(u => u.PasswordHash));   // ignore field

// With options
actual.Should().BeEquivalentTo(expected, opts => opts
    .Excluding(x => x.Timestamp)
    .ComparingByMembers<MyType>()
    .WithStrictOrdering()
);

Options control: Excluding, Including, ComparingByMembers, WithStrictOrdering, WithoutStrictOrdering, IgnoringCyclicReferences.

references

matchers.md

SKILL.md

tile.json