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fluent-asserts

Installation

The easiest way to use fluent-asserts is through DUB, the D package manager.

dependency "fluent-asserts" version="~>2.0"

Then run:

Terminal window
dub build

Supported Compilers

fluent-asserts works with:

  • DMD (Digital Mars D Compiler) - Reference compiler
  • LDC (LLVM D Compiler) - Recommended for production
  • GDC (GNU D Compiler)

Basic Usage

Once installed, import the library and start writing assertions:

import fluent.asserts;


unittest {
    // Basic equality
    expect("hello").to.equal("hello");


    // Numeric comparisons
    expect(42).to.be.greaterThan(10);
    expect(3.14).to.be.approximately(3.1, 0.1);


    // String operations
    expect("hello world").to.contain("world");


    // Collections
    expect([1, 2, 3]).to.contain(2);


    // Exception testing
    expect({
        throw new Exception("error");
    }).to.throwException!Exception;
}

Running Tests

Terminal window
# Run all tests
dub test


# Run tests with a specific compiler
dub test --compiler=ldc2

Release Builds

By default, fluent-asserts assertions are disabled in release builds (similar to D’s built-in assert). This means you can use fluent-asserts in production code without runtime overhead in release builds.

See Configuration for details on how to control this behavior.

Integration with Test Frameworks

fluent-asserts integrates seamlessly with D test frameworks.

Trial is an extensible test runner for D that pairs perfectly with fluent-asserts. It provides test discovery, custom reporters, and filtering capabilities.

Add trial to your project:

dependency "fluent-asserts" version="~>2.0"
dependency "trial" version="~>0.8.0-beta.7"

Run your tests with:

Terminal window
dub run trial

Filter tests by name:

Terminal window
dub run trial -- -t "test name pattern"

Trial discovers tests from unittest blocks and supports naming them with @("name") attributes or /// doc comments.

Naming Tests with Doc Comments

Use /// doc comments above your tests. Trial displays these in the test output:

import fluent.asserts;


/// user registration requires a valid email
unittest {
    expect({
        registerUser("invalid-email");
    }).to.throwException!ValidationError;
}


/// passwords are hashed before storage
unittest {
    auto user = createUser("test@example.com", "password123");
    expect(user.passwordHash).to.not.equal("password123");
}

BDD-Style Spec Syntax

For behavior-driven development, trial provides the Spec! template with describe, it, and beforeEach blocks:

module tests.user;


import fluent.asserts;
import trial.discovery.spec;


alias suite = Spec!({
    describe("User", {
        int age;


        beforeEach({
            age = 21;
        });


        describe("age validation", {
            it("accepts adults", {
                expect(isAdult(age)).to.equal(true);
            });


            it("rejects minors", {
                age = 16;
                expect(isAdult(age)).to.equal(false);
            });
        });
    });
});

Built-in Unittests

unittest {
    expect(1 + 1).to.equal(2);
}

Unit-threaded

import unit_threaded;
import fluent.asserts;


@("my test")
unittest {
    expect(getValue()).to.equal(42);
}

Silly

import silly;
import fluent.asserts;


@("calculates correctly")
unittest {
    expect(calculate(2, 3)).to.equal(5);
}

Upgrading from v1.x

If you’re upgrading from fluent-asserts v1.x, see the Upgrading to v2.0.0 guide for migration steps and breaking changes.

Next Steps