TinyBDD — Fluent BDD for .NET, zero ceremony

Write expressive Given/When/Then tests that feel great and run anywhere (xUnit, NUnit, MSTest) without framework lock-in.

Why TinyBDD

• Tiny core you can read in minutes
• Fluent, async-first chains (Given/When/Then/And/But)
• Deferred fluent expectations (Expect.For/That) — compose reasons/hints, throw only when awaited
• Automatic Step IO lineage (inputs/outputs + current item tracked)
• Works with any assertion library
• Adapters for xUnit, NUnit, MSTest (optional)
• Gherkin-style reporting to your test output

Try it in 30 seconds

Ambient (with adapter base class or Ambient.Current set):

await Given(() => 1)
     .When("double", x => x * 2)
     .Then("== 2", v => v == 2)
     .AssertPassed();

Explicit (no base class required):

var ctx = Bdd.CreateContext(this);
await Bdd.Given(ctx, "numbers", () => new[]{1,2,3})
         .When("sum", (arr, _) => Task.FromResult(arr.Sum()))
         .Then("> 0", sum => sum > 0)
         .AssertPassed();

Documentation Map

• Introduction: introduction.md
• Getting Started: getting-started.md
• Fundamentals (BDD & Gherkin): bdd-fundamentals.md
• BDD + TDD Workflow: tdd-via-bdd.md
• Expectations & Assertions: assertions-and-expectations.md
• Step IO & State Tracking: step-io-and-state.md
• Tips & Tricks: tips-and-tricks.md
• Extensibility & Advanced: advanced-usage.md

Tip: add [Feature], [Scenario], and [Tag] to make reports shine. Base classes emit Gherkin output automatically.