How to Effectively Mock `c.BindQuery` and Service Calls in Gin Handler Function Unit Tests?

Mocking c.BindQuery in Gin Handler Function Unit Tests

Unit testing Go Gin handler functions often involves mocking certain operations to isolate and test specific scenarios. One such operation is c.BindQuery, which binds request query string parameters to a given struct.

When testing GetMaterialByFilter, the test would fail due to an error related to invalid memory access or nil pointer dereference. This error stems from the fact that c.BindQuery was not properly initialized with a valid HTTP request.

To mock c.BindQuery, create an http.Request and set its URL and URL.RawQuery fields. This allows you to simulate the request that would be received by the handler function:

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{/* ... */}

    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
}

Testing Service Calls

The handler function also makes a call to a service method, services.WeldprogService.GetMaterialByFilter. To test this call, the service must be injectable, either through the handler function signature or by setting it as a Gin context value.

If the service is an interface, it can be injected using the c.Set method:

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)
}

Mock the service in the unit tests by implementing the required interface and setting it as the service context value:

type mockSvc struct {}

func (mockSvc) GetMaterialByFilter(*weldprogs.QueryParam) (*materialByFilter, error) { /* ... */}

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

    c.Set("svc_context_key", &mockSvc{})

    GetMaterialByFilter(c)
    // ... 
}

By following these steps, you can effectively mock both c.BindQuery and service calls to isolate and thoroughly test your Gin handler function.

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