Build Mock APIs in Go


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HTTP Mocking Tool for Go


HTTP server mocking tool for Go.
Mocha creates a real HTTP server and lets you configure response stubs for HTTP Requests when it matches a set of matchers. It provides a functional like API that allows you to match any part of a request against a set of matching functions that can be composed.

Inspired by WireMock and Nock.


go get


  • Configure HTTP response stubs for specific requests based on a criteria set.
  • Matches request URL, headers, queries, body.
  • Stateful matches to create scenarios, mocks for a specific number of calls.
  • Response body template.
  • Response delays.
  • Run in your automated tests.

How It Works

Mocha works by creating a real HTTP Server that you can configure response stubs for HTTP requests when they match a set request matchers. Mock definitions are stored in memory in the server and response will continue to be served as long as the requests keep passing the configured matchers.
The basic is workflow for a request is:

  • run configured middlewares
  • mocha parses the request body based on:
  • custom RequestBodyParser configured
  • request content-type
  • mock http handler tries to find a mock for the incoming request were all matchers evaluates to true
  • if all matchers passes, it will use mock reply implementation to build a response
  • if no mock is found, it returns an HTTP Status Code 418 (teapot).
  • after serving a mock response, it will run any PostAction configured.

Getting Started

Usage typically looks like the example below:

func Test_Example(t *testing.T) {
    m := mocha.New(t)

    scoped := m.AddMocks(mocha.Get(expect.URLPath("/test")).
        Header("test", expect.ToEqual("hello")).
        Query("filter", expect.ToEqual("all")).
        Reply(reply.Created().BodyString("hello world")))

    req, _ := http.NewRequest(http.MethodGet, m.URL()+"/test?filter=all", nil)
    req.Header.Add("test", "hello")

    res, err := http.DefaultClient.Do(req)
    if err != nil {

    body, err := ioutil.ReadAll(res.Body)

    assert.Nil(t, err)
    assert.True(t, scoped.Called())
    assert.Equal(t, 201, res.StatusCode)
    assert.Equal(t, string(body), "hello world")


Mocha has two ways to create an instance: mocha.New() and mocha.NewSimple().
mocha.NewSimple() creates a new instance with default values for everything.
mocha.New(t, ...config) needs a mocha.T implementation and allows to configure the mock server. You use testing.T implementation. Mocha will use this to log useful information for each request match attempt. Use mocha.Configure() or provide a mocha.Config to configure the mock server.

Request Matching

Matchers can be applied to any part of a Request and Mocha provides a fluent API to make your life easier.
See usage examples below:

Method and URL

m := mocha.New(t)


m := mocha.New(t)
    Header("test", expect.ToEqual("hello")))


m := mocha.New(t)
    Query("filter", expect.ToEqual("all")))


Matching JSON Fields

m := mocha.New(t)
        expect.JSONPath("name", expect.ToEqual("dev")), expect.JSONPath("ok", expect.ToEqual(true))).

Form URL Encoded Fields

    FormField("field1", expect.ToEqual("dev")).
    FormField("field2", expect.ToContain("qa")).


You can define a response that should be served once a request is matched.
Mocha provides several ways to configure a reply.
The built-in reply features are:

Replies are based on the Reply interface.
It's also possible to configure response bodies from templates. Mocha uses Go Templates. Replies usage examples:

Basic Reply

m := mocha.New(t)

Replies In Sequence

m := mocha.New(t)
        Add(InternalServerError(), BadRequest(), OK(), NotFound())))

Random Replies

m := mocha.New(t)
        Add(reply.BadRequest(), reply.OK(), reply.Created(), reply.InternalServerError())))

Reply Function

m := mocha.New(t)
    ReplyFunction(func(r *http.Request, m mocha.M, p params.P) (*mocha.Response, error) {
        return &mocha.Response{Status: http.StatusAccepted}, nil

Reply From Forwarded Request

reply.From will forward the request to the given destination and serve the response from the forwarded server.
It`s possible to add extra headers to the request and the response and also remove unwanted headers.

m := mocha.New(t)
        ProxyHeader("x-proxy", "proxied").
        Header("x-res", "response"))

Body Template

Mocha comes with a built-in template parser based on Go Templates.
To serve a response body from a template, follow the example below:

templateFile, _ := os.Open("template.tmpl"))
content, _ := ioutil.ReadAll(templateFile)

m := mocha.New(t)
            FuncMap(template.FuncMap{"trim": strings.TrimSpace}).

Specifying Headers

m := mocha.New(t)
    Reply(reply.OK().Header("test", "test-value"))

Delay Responses

You can configure a delay to responses to simulate timeouts, slow requests and any other timing related scenarios.
See the example below:

delay := time.Duration(1250) * time.Millisecond



Mocha Instance

Mocha instance provides methods to assert if associated mocks were called or not, how many times they were called, allows you to enable/disable then and so on.
The available assertion methods on mocha instance are:

  • AssertCalled: asserts that all associated mocks were called at least once.
  • AssertNotCalled: asserts that associated mocks were not called.
  • AssertHits: asserts that the sum of calls is equal to the expected value.


Mocha instance method AddMocks returns a Scoped instance that holds all mocks created.
Scopes allows you control related mocks, enabling/disabling, checking if they were called or not. Scoped instance also provides assertions to facility tests verification. See below the available test assertions:

  • AssertCalled: asserts that all associated mocks were called at least once.
  • AssertNotCalled: asserts that associated mocks were not called.


Mocha provides several matcher functions to facilitate request matching and verification. See the package expect for more details.
You can create custom matchers using these two approaches:

  • create a expect.Matcher struct
  • use the function expect.Func providing a function with the following signature: func(v any, a expect.Args) (bool, error)

Matcher Composition

It's possible to compose multiple matchers.
Every matcher has a .And(), .Or() and a .Xor() that allows composing multiple matchers.
See the example below:


BuiltIn Matchers

| Matcher | Description | | ------------ | --------------------------------------------------------------------------------------------------- | | AllOf | Returns true when all given matchers returns true | | AnyOf | Returns true when any given matchers returns true | | Both | Returns true when both matchers returns true | | ToContain | Returns true when expected value is contained on the request value | | Either | Returns true when any matcher returns true | | ToBeEmpty | Returns true when request value is empty | | ToEqual | Returns true when values are equal | | ToEqualFold | Returns true when string values are equal, ignoring case | | ToEqualJSON | Returns true when the expected struct represents a JSON value | | Func | Wraps a function to create a inline matcher | | ToHaveKey | Returns true if the JSON key in the given path is present | | ToHavePrefix | Returns true if the matcher argument starts with the given prefix | | ToHaveSuffix | Returns true when matcher argument ends with the given suffix | | JSONPath | Applies the provided matcher to the JSON field value in the given path | | ToHaveLen | Returns true when matcher argument length is equal to the expected value | | LowerCase | Lower case matcher string argument before submitting it to provided matcher. | | UpperCase | Upper case matcher string argument before submitting it to provided matcher | | ToMatchExpr | Returns true then the given regular expression matches matcher argument | | Not | Negates the provided matcher | | Peek | Will return the result of the given matcher, after executing the provided function | | ToBePresent | Checks if matcher argument contains a value that is not nil or the zero value for the argument type | | Trim | Trims' spaces of matcher argument before submitting it to the given matcher | | URLPath | Returns true if request URL path is equal to the expected path, ignoring case | | XOR | Exclusive "or" matcher |

Future Plans

  • [ ] Configure mocks with JSON/YAML files
  • [ ] CLI
  • [ ] Docker
  • [ ] Proxy and Record


Check our Contributing guide for more details.


FOSSA Status

This project is MIT Licensed.

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