## Preface
In other languages, testing libraries exist which allow you to "mock" a
function (see <https://jestjs.io/docs/mock-functions>).
Mocking a function means swapping out a function your program would normally
call, with another function. E.g. it would find all invocations of `foo()` and
swap it out with a test function you've written `fooMock()`
This is very powerful for testing purposes, and is why I am trying to replicate
this behavior.
Elegantbeef and I have been talking about this in chat for a while, and have
been testing solutions such as using (or abusing) TRMs with little success.
## Examples of what I'd like to have
### `strgen.nim`
import std/[random]
randomize()
proc genString*(length: int): string =
for i in 0 ..< length:
result &= rand('a'..'z')
Run
### `strgen_test.nim`
import strgen
mock(strgen.genString, proc(length: int): string = "foobar")
assert strgen(12).len == 6
mock(strgen.genString, proc(length: int): string = "foobarbaz")
assert strgen(12).len == 9
Run
You'll notice that `strgen` would normally output strings with a length of `12`
here, but that changes because of the mocks. These are also able to be declared
and changed at runtime.
I'm hoping some members of the community could help brainstorm a way for this
to be achieved. Some of the solutions we've thought of so far have greatly
restricted the desired flexibility of "mocking", or would require compiler
changes.
