# ExStub
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[](https://hex.pm/packages/ex_stub)
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[](http://inch-ci.org/github/oarrabi/ex_stub)
`ExStub` provides an easy way to stub a module and record the function calls on it.
## Installation
Add `ex_stub` to your deps in `mix.exs` as a development dependency.
```elixir
def deps do
[{:ex_stub, "~> 0.1.0", only: :test}]
end
```
## Usage
If you have a module in your original application like:
```elixir
defmodule OriginalModule do
def process(param), do: :original_process
def another_method, do: :original_method
end
```
You can quickly create a stub copy of this module using `defstub`
```elixir
use ExStub
defstub MyStub, for: OriginalModule do
def process(true), do: :stubbed1
def process(false), do: :stubbed2
def process(1), do: :stubbed3
end
```
Now you can pass around `MyStub` instead of `OriginalModule`.
When you invoke method from the created `MyStub`, if the method was stubbed it will call the stubbed version.
Else the original version will be called.
```elixir
MyStub.process(true) # returns :stubbed1
MyStub.process(false) # returns :stubbed2
MyStub.process(1) # returns :stubbed3
MyStub.process(20) # returns :original_process
MyStub.another_method # returns :original_method
```
Notice that Since we did not stub `another_method`, calling it on `MyStub` returns the original implementation.
Also when calling `MyStub.process(20)` the original implementation is called since it failed pattern matching with our stub version of the method.
----
As a safety procedure, if you try to stub a method that is not found in the original module. ExStub will throw a compilation error telling you about the unexpected stubbed method.
```elixir
defstub MyStub, for: OriginalModule do
def new_method(), do: :stubbed1
end
```
The following error will be thrown
```
** (RuntimeError) Cannot provide implementations for methods that are not in the original module
The def `{:new_method, 0}` is not defined in module `OriginalModule`
```
## Recording method calls
All the functions called on the `defstub` created module will be recorded.
To get all the functions calls on `YourModule` module
```elixir
ExStub.Recorder.calls(YourModule)
```
To get all the `:the_method` function calls on `YourModule`
```elixr
ExStub.Recorder.calls(YourModule, :the_method)
```
Alternativey, you can use `assert_called` in your unit tests:
The syntax is `assert_called ModuleName.function_name(params)`
```elixir
# No parameters
assert_called ModuleName.function_name
# nil passed
assert_called ModuleName.function_name(nil)
# multiple parameters
assert_called ModuleName.function_name(1, 2)
```
Some more examples
```elixir
MyStub.process(1)
# Passes since we called the function with [1]
assert_called MyStub.process(1)
# Fails since the parameters dont match
assert_called MyStub.process(1, 2)
# Fails since we did not call `another_method`
assert_called MyStub.another_method
```
