# Schism

Schism provides a simple api for testing partitions between BEAM nodes.

Documentation: [https://hexdocs.pm/schism](https://hexdocs.pm/schism).

## Installation

If [available in Hex](https://hex.pm/docs/publish), the package can be installed
by adding `schism` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:schism, "~> 1.0", only: [:dev, :test]}
  ]
end
```

## Usage

Let's say that we have 5 nodes and we want to test what happens when they
disconnect from each other. We can use schism like so:

```elixir
test "netsplits" do
  [n1, n2, n3, n4, n5] = nodes

  # Partition our nodes
  Schism.partition([n1, n3])
  Schism.partition([n4])
  Schism.partition([n2, n5])

  # Test some stuff...

  # Heal our partitions
  Schism.heal([n1, n3])
  Schism.heal([n2, n4, n5])
end
```

This api is useful for testing and development in conjunction with tools like
[local cluster](https://github.com/whitfin/local-cluster) and [propcheck](https://github.com/alfert/propcheck).

It is not recommended that you use this in production.

## Things Schism doesn't do

Schism's reason for existing is to quickly and easily test netsplits between BEAMS
and it uses a rudimentary trick with cookies to achieve this goal. This is great
for quickly testing your system against faults.

But because of Schism's simple nature it should not be considered a replacement
for a more robust suite of tests. It *does not* test failed TCP connections,
interleaving of messages, race-conditions, clock skew, corruption, or any of
the other issues you will see in a distributed system.