Unit tests mock an interface from struct property - go

Question

I want to mock a property from a struct that uses an interface so I don't get a nil pointer when the function arrives at that point.
This is the code:
type Server struct{
parser: Parser
}
type Parser interface{
SetProvider(p *Provider)
}
func (s *Server) doSomething(){
s.anotherAction()
// ...
// here it crashes because I haven't assigned anything to parser in serverMock
s.parser.SetProvider(&Provider{
name: "foo"
})
}
And this the test code:
var serverMock = &Server{
parser:
}
// mock SetProvider
func (s *Server) SetProvider(p *Provider) {
// some action
}
TestMyCustomTest(){
res, err := serverMock.doSomething()
expected := struct{
hobby: "code",
}
assert.Equal(t, &expected, res)
}
As you see I haven't assigned anything to parser: from var serverMock because I still don't know what should I do to make it work. I cannot assign a mockInterface to that parser field because it'll tell me that the original Server struct requires the Parser interface not a mock one and I think I need the &Server pointer for var serverMock = &Server because it's using other actions like s.anotherAction().

Answer 1

If i understand your intention correctly, you want to test Server's doSomething method and it depends on Parser.SetProvider method. So, what you want, instead of mocking Server, is to create mock struct that satisfies Parser interface and create Server instance that uses it. Here is example of such test:
type mockParser struct {
// You can add field here
}
// mockParser implements SetProvider(p *Provider) method so that it satisfies Parser interface
func (parser *mockParser) SetProvider(provider *Provider) {
// You can do something here
}
TestMyCustomTest(t *testing.T){
parser := mockParser{}
srv := &Server{parser: &parser}
// write your test
assert.Equal(t, ...)
}