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How to mock standard library functions in D

I have a function that calls isFile (from std.file) on a filename and then proceeds appending .1, .2, .3 etc, checking whether each one of those is present.

I want to unit test the function, but to do so I need to mock isFile.

I looked around a bit and I found ways to mock classes but not single functions.

Solution

  • Since my answer is slightly different from Adam's, I will add it, and he can add his.

    You can use "Scoped imports" for that purpose. See the respective section in the documentation http://dlang.org/module.html

    Here's also a working example, how you can mock an isFile function inside a unittest block (assuming it is defined in module "mocks") 

    import std.file; 
import std.stdio;

int main(string[] args) 
{ 
    writeln(isFile("qq.d")); 
    return 0; 
} 

unittest 
{ 
    import mocks;
    writeln(isFile("qq.d")); 
}