Allows Julia function calls to be temporarily overloaded for purpose of testing.
Suppose you wrote the function randdev
(UNIX only). How would you go about writing tests
for it?
function randdev(n::Integer)
open("/dev/urandom") do fp
reverse(read(fp, n))
end
end
The non-deterministic behaviour of this function makes it hard to test but we can write some tests dealing with the deterministic properties of the function:
using Test
using ...: randdev
n = 10
result = randdev(n)
@test eltype(result) == UInt8
@test length(result) == n
How could we create a test that shows the output of the function is reversed? Mocking.jl
provides the @mock
macro which allows package developers to temporarily overload a
specific calls in their package. In this example we will apply @mock
to the open
call
in randdev
:
using Mocking
function randdev(n::Integer)
@mock open("/dev/urandom") do fp
reverse(read(fp, n))
end
end
With the call site being marked as "mockable" we can now write a testcase which allows
us to demonstrate the reversing behaviour within the randdev
function:
using Mocking
using Test
using ...: randdev
Mocking.activate() # Need to call `activate` before executing `apply`
n = 10
result = randdev(n)
@test eltype(result) == UInt8
@test length(result) == n
# Produces a string with sequential UInt8 values from 1:n
data = unsafe_string(pointer(convert(Array{UInt8}, 1:n)))
# Generate a alternative method of `open` which call we wish to mock
patch = @patch open(fn::Function, f::AbstractString) = fn(IOBuffer(data))
# Apply the patch which will modify the behaviour for our test
apply(patch) do
@test randdev(n) == convert(Array{UInt8}, n:-1:1)
end
# Outside of the scope of the patched environment `@mock` is essentially a no-op
@test randdev(n) != convert(Array{UInt8}, n:-1:1)
Remember to:
- Use
@mock
at desired call sites - Run
Mocking.activate()
before executing anyapply
calls
The @mock
macro uses a conditional check of Mocking.activated()
which only allows
patches to be utilized only when Mocking has been activated. By default, Mocking starts as
disabled which should result conditional being optimized away allowing for zero-overhead.
Once activated via Mocking.activate()
the Mocking.activated
function will be
re-defined, causing all methods dependent on @mock
to be recompiled.
Mocking.jl is provided under the MIT "Expat" License.