On Wednesday, 22 August 2018 at 08:33:36 UTC, Andrey wrote:
Hello,
I know that D has build-in unit tests. If so, what mechanism D
provides for mocking objects?
For example:
struct WebParser
{
// ...
int download(string path)
{
SomeHttpClient client(path);
auto result = client.request(path, 10, "Qwerty");
// ...
return result.getSomething();
}
}
Here I want to replace struct/class SomeHttpClient from
3d-party library with my own test implementation. Something
like this maybe:
unittest
{
SomeMagicMockMechanism!(SomeHttpClient, MyMockedClient);
WebParser parser;
auto value = parser.download("www.example.com"); // uses
MyMockedClient.request
assert(value == 10);
}
You could also create an interface IHttpClient, a class
HttpClientProductive which forwards the calls to SomeHttpClient
and a class HttpClientDummy which can be instrumented which data
it should return in unit test case. Both classes implements the
interface.
You also need a way to set the productive class for productive
scenario and the dummy class in test scenario, e.g. via a factory
class.
There is a huge benefit using this way, you have a very loose
coupling to SomeHttpClient. You can replace it very easily with
another library.
You could use this approach also for file system access,
environment variables access, databases...
Kind regards
Andre
