• Andrey (15/26) Aug 22 2018 Hello,
• Simen =?UTF-8?B?S2rDpnLDpXM=?= (7/36) Aug 22 2018 The language itself does not offer mocking capabilities. However,
• Andre Pany (16/45) Aug 22 2018 You could also create an interface IHttpClient, a class
• Jesse Phillips (4/7) Aug 23 2018 I'd like to pose the question, what are you testing. This looks

Andrey <saasecondbox yandex.ru> writes:

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);

}

Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:

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);

 }

The language itself does not offer mocking capabilities. However, 
there are excellent libraries in Dub:

https://code.dlang.org/packages/unit-threaded
https://code.dlang.org/packages/dmocks

--
   Simen

Andre Pany <andre s-e-a-p.de> writes:

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

Jesse Phillips <Jesse.K.Phillips+D gmail.com> writes:

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?

I'd like to pose the question, what are you testing. This looks 
like you are testing that your mocked object returns 10. I 
usually try to make functions more pure like.