nil_test.go

We can also create tests that are not specific to any particular source file; the only criteria is that the filename needs to have the <text>_test.go form. The tests in nil_test.go elucidate on some useful features of the language which the developer might find useful while writing tests. They are as follows:

• httptest.NewServer: Imagine the case where we have to test our code against a server that sends back some data. Starting and coordinating a full blown server to access some data is hard. The http.NewServer solves this issue for us.
• t.Helper: If we use the same logic to pass or fail a lot of testCases, it would make sense to segregate this logic into a separate function. However, this would skew the test run call stack. We can see this by commenting t.Helper() in the tests and rerunning go test.

We can also format our command-line output to print pretty results. We will show a simple example of adding a tick mark for passed cases and cross mark for failed cases.

In the test, we will run a test server, make GET requests on it, and then test the expected output versus actual output:

// nil_test.go 
 
package main 
 
import ( 
    "fmt" 
    "io/ioutil" 
    "net/http" 
    "net/http/httptest" 
    "testing" 
) 
 
const passMark = "\u2713" 
const failMark = "\u2717" 
 
func assertResponseEqual(t *testing.T, expected string, actual string) { 
    t.Helper() // comment this line to see tests fail due to 'if expected != actual' 
    if expected != actual { 
        t.Errorf("%s != %s %s", expected, actual, failMark) 
    } else { 
        t.Logf("%s == %s %s", expected, actual, passMark) 
    } 
} 
 
func TestServer(t *testing.T) { 
    testServer := httptest.NewServer( 
        http.HandlerFunc( 
            func(w http.ResponseWriter, r *http.Request) { 
                path := r.RequestURI 
                if path == "/1" { 
                    w.Write([]byte("Got 1.")) 
                } else { 
                    w.Write([]byte("Got None.")) 
                } 
            })) 
    defer testServer.Close() 
 
    for _, testCase := range []struct { 
        Name     string 
        Path     string 
        Expected string 
    }{ 
        {"Request correct URL", "/1", "Got 1."}, 
        {"Request incorrect URL", "/12345", "Got None."}, 
    } { 
        t.Run(testCase.Name, func(t *testing.T) { 
            res, err := http.Get(testServer.URL + testCase.Path) 
            if err != nil { 
                t.Fatal(err) 
            } 
 
            actual, err := ioutil.ReadAll(res.Body) 
            res.Body.Close() 
            if err != nil { 
                t.Fatal(err) 
            } 
            assertResponseEqual(t, testCase.Expected, fmt.Sprintf("%s", actual)) 
        }) 
    } 
    t.Run("Fail for no reason", func(t *testing.T) {
        assertResponseEqual(t, "+", "-")
    })
}