du0173
2017-08-21 03:58
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如何在Go lang中模拟exec.Command进行多个单元测试?

I just learnt unit testing functions that uses exec.Command() i.e., mocking exec.Command(). I went ahead to added more unit cases, but running into issues of not able to mock the output for different scenarios.

Here is a sample code hello.go I'm trying to test...

package main

import (
    "fmt"
    "os/exec"
)

var execCommand = exec.Command

func printDate() ([]byte, error) {
    cmd := execCommand("date")
    out, err := cmd.CombinedOutput()
    return out, err
}

func main() {
    fmt.Printf("hello, world
")
    fmt.Println(printDate())
}

Below is the test code hello_test.go...

package main

import (
    "fmt"
    "os"
    "os/exec"
    "testing"
)

var mockedExitStatus = 1
var mockedDate = "Sun Aug 20"
var expDate = "Sun Aug 20"

func fakeExecCommand(command string, args ...string) *exec.Cmd {
    cs := []string{"-test.run=TestHelperProcess", "--", command}
    cs = append(cs, args...)
    cmd := exec.Command(os.Args[0], cs...)
    cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
    return cmd
}

func TestHelperProcess(t *testing.T) {
    if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
        return
    }

    // println("Mocked Data:", mockedDate)
    fmt.Fprintf(os.Stdout, mockedDate)
    os.Exit(mockedExitStatus)
}

func TestPrintDate(t *testing.T) {
    execCommand = fakeExecCommand
    defer func() { execCommand = exec.Command }()

    out, err := printDate()
    print("Std out: ", string(out))
    if err != nil {
        t.Errorf("Expected nil error, got %#v", err)
    }
    if string(out) != expDate {
        t.Errorf("Expected %q, got %q", expDate, string(out))
    }
}

func TestPrintDateUnableToRunError(t *testing.T) {
    execCommand = fakeExecCommand
    defer func() { execCommand = exec.Command }()

    mockedExitStatus = 1
    mockedDate = "Unable to run date command"
    expDate = "Unable to run date command"

    out, err := printDate()
    print("Std out: ", string(out))
    if err != nil {
        t.Errorf("Expected nil error, got %#v", err)
    }
    if string(out) != expDate {
        t.Errorf("Expected %q, got %q", expDate, string(out))
    }
}

go test fails for the second test TestPrintDateUnableToRunError...

$ go test hello
Std out: Sun Aug 20Std out: Sun Aug 20--- FAIL: TestPrintDateTomorrow (0.01s)
    hello_test.go:62: Expected "Unable to run date command", got "Sun Aug 20"
FAIL
FAIL    hello   0.017s

Even though I'm trying to set the global mockedDate value inside the test case, it's still getting the global value that it was initialized with. Is the global value not getting set? Or the changes to that global var is not getting updated in TestHelperProcess?

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