hat

hat

hat is an HTTP API testing framework for Go.

It's based on composable, reusable response assertions, and request modifiers. It can dramatically reduce API testing code, while improving clarity of test code and test output. It leans on the standard net/http package as much as possible.

Import as go.coder.com/hat.

Example

Let's test that twitter is working:

func TestTwitter(tt *testing.T) {
    t := hat.New(tt, "https://twitter.com")

    t.Get(
        hat.Path("/realDonaldTrump"),
    ).Send(t).Assert(t,
        asshat.StatusEqual(http.StatusOK),
        asshat.BodyMatches(`President`),
    )
}

Table of Contents generated with DocToc

• hat
  • Example
  • Basic Concepts
    • Creating Requests
    • Sending Requests
    • Reading Responses
  • Competitive Comparison
    • API Symbols
    • LoC
    • net/http
    • Chaining APIs
  • Design Patterns
    • Format Agnostic
    • Minimal API
    • testing.TB instead of *hat.T

Basic Concepts

Creating Requests

hat's entrypoint is its New method

func New(t *testing.T, baseURL string) *T

which returns a hat.T that embeds a testing.T, and provides a bunch of methods such as Get, Post, and Patch to generate HTTP requests. Each request method looks like

func (t *T) Get(opts ...RequestOption) Request

RequestOption has the signature

type RequestOption func(t testing.TB, req *http.Request)

Sending Requests

Each request modifies the request however it likes. A few common RequestOptions are provided in the hat package.

Once the request is built, it can be sent

func (r Request) Send(t *T) *Response

or cloned

func (r Request) Clone(t *T, opts ...RequestOption) Request

Cloning is useful when a test is making a slight modification of a complex request.

Reading Responses

Once you've sent the request, you're given a hat.Response. The Response should be asserted.

func (r Response) Assert(t testing.TB, assertions ...ResponseAssertion) Response

ResponseAssertion looks like

type ResponseAssertion func(t testing.TB, r Response)

A bunch of pre-made response assertions are available in the asshat package.

Competitive Comparison

It's difficult to say objectively which framework is the best. But, no existing framework satisfied us, and we're happy with hat.

LoC was calculated with cloc.

Will add more columns and libraries on demand.

API Symbols

Smaller APIs are easier to use and tend to be less opinionated.

LoC

Smaller codebases have less bugs and are easier to contribute to.

net/http

We prefer to use net/http.Request and net/http.Response so we can reuse the knowledge we already have. Also, we want to reimplement its surface area.

Chaining APIs

Chaining APIs look like

 m.GET("/some-path").
        Expect().
        Status(http.StatusOK)

We dislike them because they make custom assertions and request modifiers a second-class citizen to the assertions and modifiers of the package. This encourages the framework's API to bloat, and discourages abstraction on part of the user.

Design Patterns

Format Agnostic

hat makes no assumption about the structure of your API, request or response encoding, or the size of the requests or responses.

Minimal API

hat and asshat maintains a very small base of helpers. We think of the provided helpers as primitives for organization and application-specific helpers.

Always Fatal

While some assertions don't invalidate the test, we typically don't mind if they fail the test immediately.

To avoid the API complexity of selecting between Errors and Fatals, we fatal all the time.

testing.TB instead of *hat.T

When porting your code over to hat, it's better to accept a testing.TB than a *hat.T or a *testing.T.

Only accept a *hat.T when the function is creating additional requests. This makes the code less coupled, while clarifying the scope of the helper.

This pattern is used in hat itself. The ResponseAssertion type and the Assert function accept testing.TB instead of a concrete *hat.T or *testing.T. At first glance, it seems like wherever the caller is using a ResponseAssertion or Assert, they would have a *hat.T.

In reality, this choice lets consumers hide the initialization of hat.T behind a helper function. E.g:

func TestSomething(t *testing.T) {
	makeRequest(t,
		hat.Path("/test"),
	).Assert(t,
		asshat.StatusEqual(t, http.StatusOK),
	)
}