# Syringe
Syringe is a injection framework that also opens the opportunity for
clearer mocking and to run mocked test asynchronously.
To use the injector, it behaves similar to ```alias```, except you use the word ```inject```.
### Example
```elixir
defmodule MyThing do
def do_mine_things do
1 + 2
end
end
defmodule MyModule do
use Injector
inject MyThing, as: Mine
def do_things do
Mine.do_mine_things
end
end
```
Now that we are injecting our module we can mock it in test.
```elixir
defmodule MyModuleTest do
use ExUnit.Case, async: true
import Mocker # need this to use easy mocking functions
test "Mine must be called" do
mock(MyThing)
MyModule.do_things
assert was_called(MyThing, :do_mine_things, nil) == once # success
end
end
```
You can even take control and handle how the mocked functions can fit your test data
```elixir
defmodule MyModuleTest do
use ExUnit.Case, async: true
import Mocker
test "Mine must be called" do
mock(MyThing)
assert MyModule.do_things == nil
intercept(MyThing, :do_mine_things, nil, with: fn() -> "my mocked return" end)
assert MyModule.do_things == "my mocked return"
assert was_called(MyThing, :do_mine_things, nil) == twice # success
end
end
```
You can also just call the original function if you want.
```elixir
defmodule MyModuleTest do
use ExUnit.Case, async: true
import Mocker
test "Mine must be called" do
mock(MyThing)
assert MyModule.do_things == nil
intercept(MyThing, :do_mine_things, nil, with: :original_function)
assert MyModule.do_things == 3
assert was_called(MyThing, :do_mine_things, nil) == twice # success
end
end
```
It gets better, you can control the order in which the functions return data.
```elixir
defmodule MyModuleTest do
use ExUnit.Case, async: true
import Mocker
test "Mine must be called" do
mock(MyThing)
assert MyModule.do_things == nil
intercept(MyThing, :do_mine_things, nil, with: fn -> "do the things" end)
intercept(MyThing, :do_mine_things, nil, with: fn -> "do some other things" end)
intercept(MyThing, :do_mine_things, nil, with: :original_function)
intercept(MyThing, :do_mine_things, nil, with: fn -> "one more thing" end)
assert MyModule.do_things == "do the things"
assert MyModule.do_things == "do some other things"
assert MyModule.do_things == 3
assert MyModule.do_things == "one more thing"
# The last specified intercept will persist
assert MyModule.do_things == "one more thing"
assert MyModule.do_things == "one more thing"
assert was_called(MyThing, :do_mine_things, nil) == times(6) # success
end
end
```
Finally you can match against function arguments.
```elixir
defmodule MyThing do
def do_mine_things(arg1, arg2, arg3) do
{arg1, arg2, arg3}
end
end
defmodule MyModuleTest do
use ExUnit.Case, async: true
import Mocker
test "Mine must be called with correct arguments" do
mock(MyThing)
assert MyModule.do_things(:a, :b, :c) == nil
intercept(MyThing, :do_mine_things, [:b, :c, :d], with: fn(_, _, _) -> :ok)
intercept(MyThing, :do_mine_things, [:a, :b, :c], with: :original_function)
assert MyModule.do_things(:b, :c, :d) == :ok
assert MyModule.do_things(:a, :b, :c) == {:a, :b, :c}
MyModule.do_things(:x, :y, :z)
assert was_called(MyThing, :do_mine_things, [:b, :c, :d) == once # success
assert was_called(MyThing, :do_mine_things, [:a, :b, :c) == once # success
assert was_called(MyThing, :do_mine_things, [:x, :y, :z) == never # success
end
end
```
Sometimes you want match on any arguments
```elixir
defmodule SampleModule do
def do_some_work(how_much, call_me_when_i_am_done) do
call_me_when_i_am_done.()
end
end
defmodule ModuleImTesting do
use Injector
inject SampleModule
def do_work(how_much) do
SampleModule.do_some_work(how_much, &on_complete/0)
end
def on_complete do
IO.inspect "I'm done!"
end
end
defmodule ModuleImTestingTest do
use ExUnit.Case, async: true
import Mocker
setup do
mock(SampleModule)
:ok
end
test "should notify SampleModule to do some work" do
intercept(SampleModule, :do_some_work, [10, any], fn(_, on_complete) -> on_complete.() end) # the arguments are passed in and you can do what you want here
ModuleImTesting.do_work(10)
assert was_called(SampleModule, :do_some_work, [10, any]) == once # truthy
end
end
```
Based on the nature of how tests execute, sometimes you need to be able
to mock modules that are running in different processes. Generally used
when interacting with GenServers referred by name, but can be used
whenever things are being run in a different process than your test.
```elixir
defmodule MyWork do
def handle_work(state) do
# I'm out of fake implementations. Does it matter
# what this is at this point?
end
end
defmodule MyServer do
use GenServer
use Injector
inject MyWork
def start_link do
GenServer.start_link(__MODULE__, 0, name: __MODULE__)
end
def increment do
GenServer.call(__MODULE__, :increment)
end
def handle_call(:increment, _from, state) do
output = MyWork.handle_work(state)
{:reply, output, state}
end
end
defmodule MyServerTest do
use ExUnit.Case, async: true
use Mocker
test "should outsource work to MyWork module in the GenServer process" do
{:ok, pid} = MyServer.start_link
# now that we're operating on a different pid we need to notify the
# mocker to work within that pid
mock(MyWork, pid)
# now you can intercept the functions as before
intercept(MyWork, :handle_work, [0], fn(_) -> 100 end)
assert MyServer.increment() == 100
assert was_called(MyWork, :handle_work, [0]) == once #truthy
end
end
```
## New in version 1.2
By default, when you call `mock` on a module, it'll auto stub all function
calls and return `nil` by default. Sometimes you may have a module that
is used pretty extensively in your test and you don't want to go through
and intercept all the functions just to call the `:original_function`.
Well, you can tell the mock function to not auto mock. In your unit test,
when you call mock, just pass `no_auto_mock: true` and it'll default
to call your original_functions instead of the auto-mocked ones.
Here's an example:
Given this module:
```elixir
defmodule Foo do
def first(), do: 1
def second(), do: 2
end
defmodule Bar do
use Injector
inject Foo
def call_foo() do
a = Foo.first()
b = Foo.second()
{a, b}
end
end
defmodule BarTest do
use ExUnit.Case, async: true
import Mocker
test "foo should return a tuple of numbers" do
mock(Foo)
intercept(Foo, :first, [], with: fn() -> 100 end)
assert Bar.call_foo() == {100, nil} # nil because we didn't intercept the :second function
mock(Foo, no_auto_mock: true)
intercept(Foo, :first, [], with: fn() -> 100 end)
assert Bar.call_foo() == {100, 2} # called the original function as specified
end
end
```
## New in version 1.3
Added some new verification functions. Before version 1.3 you could only verify
if the function was exactly N times. Now you can verify at least, more than, at most,
less than, and between. Here are some examples:
```elixir
# the set up is the same
outcome = intercept(MockBar, :with_args, [any(), any(), any()], with: :original_function)
...
# now we can
assert outcome |> was_called() |> at_least(3) |> times()
assert outcome |> was_called() |> more_than(3) |> times()
assert outcome |> was_called() |> at_most(3) |> times()
assert outcome |> was_called() |> less_than(3) |> times()
assert outcome |> was_called() |> between(3..4) |> times()
```
## New in version 1.4
Added a check at test run time to verify if the intercept api arity matches
the true arity of the function. If the intercept argument count does not match
any of the functions of the same name but doesn't match the arity count, then
an error will be raised. Here's an example:
```elixir
defmodule MockBar do
def with_args(a, b) do
...
end
end
# the set up is the same
mock(MockBar)
# Raises MockerApiError, the with_args function has an arity of 2, but the intercept
# is mocking an arity of 3. This allows a developer to change the arity of a function
# and the mocker will let them know that the intercepts need to be updated as well
outcome = intercept(MockBar, :with_args, [any(), any(), any()], with: fn(_, _, _) -> :ok end)
```
Also added some convenience options for the intercept function to simplify your mocking.
You can now just tell the intercept to return a value without specifying a function or
specifying an error to raise. Here's some examples:
```elixir
# the set up is the same
mock(MockBar)
# will return foo if args match
intercept(MockBar, :with_args, [any(), any()], returns: "foo")
```
For raising errors
```elixir
defmodule SomeError do
defexception [:message]
end
mock(MockBar)
# will raise if matches args
intercept(MockBar, :with_args, [any(), any()], raises: SomeError)
```
or if you want to set a specific messages to the error
```elixir
defmodule SomeError do
defexception [:message, :more_detail]
end
mock(MockBar)
# will raise if matches args and assign the message to the :message field in the error
intercept(MockBar, :with_args, [any(), any()], raises: SomeError, message: "My special message", more_detail: "rtfm")
```
## Gotcha's/Limitations
Due to the way that syringe handles the inject as an alias, if you refer
to the full module name, syringe is unable to intercept the function
calls. Here's an example:
```elixir
defmodule Oh.My.Foo do
def bar() do
end
end
defmodule Oh.My.Bar do
use Injector
inject Oh.My.Foo
def call_foo() do
Oh.My.Foo.bar() # <-- cannot be intercepted, you must strictly call Foo.bar()
end
end
```
Sometimes you may need to mock or test modules that are GenServers that get started by the application. This can
be problematic since the Application will start before `Mocker.start_link()` gets called causing the process to
exit before the tests even start. This is only an issue during testing. The recommended approach is to not start
the workers during tests for several reasons. It makes testing the GenServers problematic in general, especially
with regards to named GenServers. You can read more into the details on this issue (https://github.com/skylerparr/syringe/issues/6).
## Installation
1. Add `syringe` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[{:syringe, "~> 1.0.0"}]
end
```
2. Configure syringe for your environments in `test/config.exs` (if you want to use mocking):
```elixir
config :syringe, injector_strategy: MockInjectingStrategy
```
in your other configs:
```elixir
config :syringe, injector_strategy: AliasInjectingStrategy
```
3. Turn on mocking for your tests. In your `test/test_helper.exs`:
```elixir
Mocker.start_link
```
4. You're ready to start injecting implementations!
