How to Mock Gin's `c.BindQuery` for Effective Unit Testing?

Mocking Gin Handler c.BindQuery for Unit Testing

Issue

A unit test for a Gin handler function GetMaterialByFilter fails when c.BindQuery is called. How can this issue be resolved by mocking the function?

Overview

The issue stems from the lack of an actual HTTP request during testing. To perform HTTP-based operations, a request must be initialized and set to the Gin context. Specifically, for c.BindQuery, proper initialization of the request's URL and URL.RawQuery is crucial.

Mock Implementation

To mock c.BindQuery, follow these steps:

1. Initialize a *gin.Context and *httptest.ResponseRecorder.
2. Create an *http.Request and set its URL and Header as needed.
3. Initialize the request query (weldprogs.QueryParam) and encode it into the URL.RawQuery.
4. Set the request to the Gin context using c.Request = req.

func mockGin() (*gin.Context, *httptest.ResponseRecorder) {
    w := httptest.NewRecorder()
    c, _ := gin.CreateTestContext(w)

    req := &http.Request{
        URL:    &url.URL{},
        Header: make(http.Header),
    }

    testQuery := weldprogs.QueryParam{/* init fields */}
    q := req.URL.Query()
    for _, s := range testQuery.Basematgroup_id {
        q.Add("basematgroup_id", s)
    }

    req.URL.RawQuery = q.Encode()
    c.Request = req

    return c, w
}

Mocking External Dependencies

Additionally, the services.WeldprogService.GetMaterialByFilter(&queryParam) call is not testable in its current form. It should be an interface and injected as a dependency of the handler.

Injecting the Dependency

func GetMaterialByFilter(c *gin.Context) {
    //...
    weldprogService := mustGetService(c)
    materialByFilter, getErr := weldprogService.GetMaterialByFilter(&queryParam)
    // ...
}

func mustGetService(c *gin.Context) services.WeldprogService {
    svc, exists := c.Get("svc_context_key")
    if !exists {
        panic("service was not set")
    }
    return svc.(services.WeldprogService)
}

Mocking the Dependency

type mockSvc struct {
}

// have 'mockSvc' implement the interface 

func TestGetMaterialByFilter(t *testing.T) {
    w := httptest.NewRecorder()
    c, _ := gin.CreateTestContext(w)

    // now you can set mockSvc into the test context
    c.Set("svc_context_key", &mockSvc{})

    GetMaterialByFilter(c)
    // ... 
}

By combining these techniques, you can effectively mock c.BindQuery and external dependencies, allowing for comprehensive unit tests of your Gin handler functions.

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