httpmock

To start mocking, call httpmock.Activate(t) within your test. You can then register responders for specific HTTP methods and URLs.

httpmock supports:

• Exact URL matching: Provide the full URL.
• Regexp matching: Use the =~ prefix in the URL string to indicate a regular expression.

You can also track call counts using httpmock.GetTotalCallCount() or httpmock.GetCallCountInfo() to verify how many times specific endpoints were hit.

func TestFetchArticles(t *testing.T) {
  httpmock.Activate(t)

  // Exact URL match
  httpmock.RegisterResponder("GET", "https://api.mybiz.com/articles",
    httpmock.NewStringResponder(200, `[{"id": 1, "name": "My Great Article"}]`))

  // Regexp match
  httpmock.RegisterResponder("GET", `=~^https://api\.mybiz\.com/articles/id/\d+\z`,
    httpmock.NewStringResponder(200, `{"id": 1, "name": "My Great Article"}`))

  // ... perform requests ...

  // get count info
  httpmock.GetTotalCallCount()
  info := httpmock.GetCallCountInfo()
  _ = info["GET https://api.mybiz.com/articles"]
}

To use httpmock, you must first activate the mock environment. This intercepts HTTP calls made via http.DefaultClient or http.DefaultTransport.

• Activate(): Starts the mock environment. It is recommended to use t.Cleanup(httpmock.Deactivate) immediately after activation in tests to ensure the environment is shut down when the test finishes.
• Deactivate(): Shuts down the mock environment and restores the original transports for all clients that were overridden using ActivateNonDefault.
• DeactivateAndReset(): A convenience method that calls both Deactivate() and Reset(). This is useful for cleaning up both the environment and the registered mocks/counters.
• Reset(): Removes all registered mocks and zeroes out call counters, but keeps the mock environment active.

func TestFetchArticles(t *testing.T) {
  httpmock.Activate()
  t.Cleanup(httpmock.Deactivate)

  // when this test ends, the mock environment will close
}

For more complex scenarios, httpmock provides several advanced capabilities:

• Custom Function Responders: Pass a function func(req *http.Request) (*http.Response, error) to RegisterResponder to implement dynamic logic.
• Regexp Submatches: Use httpmock.MustGetSubmatchAsUint(req, index) to extract values (like IDs) captured in a regex URL pattern.
• Matcher Responders: Use httpmock.RegisterMatcherResponder combined with matchers like httpmock.BodyContainsString(string) to trigger specific responses based on request body content.
• Response Helpers:
  • httpmock.NewJsonResponse(status, data): Returns a JSON response with application/json content-type.
  • httpmock.NewStringResponder(status, body): Returns a plain string response.
  • httpmock.NewStringResponse(status, body): Used within custom functions to return a response.

// Example: Using regexp submatches and custom logic
httpmock.RegisterResponder("GET", `=~^https://api\.mybiz\.com/articles/id/(\d+)\z`,
  func(req *http.Request) (*http.Response, error) {
    id := httpmock.MustGetSubmatchAsUint(req, 1)
    return httpmock.NewJsonResponse(200, map[string]interface{}{
      "id":   id,
      "name": "My Great Article",
    })
  })

// Example: Matching based on request body
httpmock.RegisterMatcherResponder("POST", "https://api.mybiz.com/articles",
  httpmock.BodyContainsString(`"type":"toy"`),
  httpmock.NewStringResponder(400, `{"reason":"Invalid article type"}`))