How to mock netconf session in unit testing Golang

Question content

I am using juniper's netconf package ("github.com/juniper/go-netconf/netconf") to establish a netconf session in my code .

I want to know how to simulate a netconf session in a unit test.

My method is:

func testmyfunction(t *testing.t) {
    getsshconnection = mockgetsshconnection
    got := myfunction()
    want := 123
    if !reflect.deepequal(got, want) {
        t.errorf("error expectation not met, want %v, got %v", want, got)
    }
}

func mockgetsshconnection() (*netconf.session, error) {
    var sess netconf.session
    sess.sessionid = 123
    return &sess, nil
}

The problem occurs when myfunction() has a line that delays sess.close() and throws an error due to a nil pointer dereference

func MyFunction() int {
    sess, err := getSSHConnection() // returns (*netconf.Session, error)
    if err == nil && sess != nil {
        defer sess.Close() -> Problem happens here
        // Calls RPC here and rest of the code here
        
    } 
    return 0
}

So, what changes can I make to the mockgetsshconnection() method so that sess.close() doesn't throw an error?

Solution

nil The pointer error originates from the close function when the underlying transport is calledclose when. Fortunately transport is an interface type that you can easily mock and use in a real instance of netconf.session. For example, like this:

type MockTransport struct{}

func (t *MockTransport) Send([]byte) error {
    return nil
}

func (t *MockTransport) Receive() ([]byte, error) {
    return []byte{}, nil
}

func (t *MockTransport) Close() error {
    return nil
}

func (t *MockTransport) ReceiveHello() (*netconf.HelloMessage, error) {
    return &netconf.HelloMessage{SessionID: 123}, nil
}

func (t *MockTransport) SendHello(*netconf.HelloMessage) error {
    return nil
}

func (t *MockTransport) SetVersion(version string) {
}

func mockGetSSHConnection() (*netconf.Session, error) {
    t := MockTransport{}
    sess := netconf.NewSession(&t)
    return sess, nil
}

Note that the function you are testing currently returns 0 instead of the sessionid of the session. Therefore, you should fix the issue before the test succeeds.

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