remiq / elixir_quickcheck_example

This repository shows how to use QuviQ’s QuickCheck Mini in Elixir.

ElixirQuickcheckExample

This repository shows how to use QuviQ’s QuickCheck Mini in Elixir.

Installation

1. Download QuickCheck Mini: http://www.quviq.com/downloads/

2. Unpack zip somewhere ie. ~/eqcmini-2.01.0/

3. Run iex in this directory

   $ cd ~/eqcmini-2.01.0/ $ sudo iex

4. Run following command in iex:

   iex(1)> :eqc_install.install() Installation program for "Quviq QuickCheck Mini" version 2.01.0. Installing in directory /usr/lib/erlang/lib. Installing ["eqc-2.01.0"]. Quviq QuickCheck Mini is installed successfully. Bookmark the documentation at /usr/lib/erlang/lib/eqc-2.01.0/doc/index.html. :ok

QuickCheck Mini is now installed on your local Erlang VM. Do it once per development machine. You don't do it in production.

Mix project changes

Add :eqc_ex dependency.

defp deps do
  [
    {:eqc_ex, "~> 1.2"}
  ]
end

Run mix deps.get and mix test. You will get following error:

== Compilation error on file lib/eqc/mocking.ex ==
** (RuntimeError) error parsing file /usr/lib/erlang/lib/eqc-2.01.0/include/eqc_mocking_api.hrl, got: {:error, :enoent}

Now, you will google and you will get this issue: Quviq/eqc_ex#3 Important part:

There is no free version with eqc_mocking in it, thus it won't work.

This means that :eqc_ex will not work with QuickCheck Mini. Or is it?

Edit deps/eqc_ex/lib/eqc/mocking.ex and comment lines 25-27:

#Record.defrecord :api_spec, Record.extract(:api_spec, from_lib: "eqc/include/eqc_mocking_api.hrl")
#Record.defrecord :api_module, Record.extract(:api_module, from_lib: "eqc/include/eqc_mocking_api.hrl")
#Record.defrecord :api_fun, Record.extract(:api_fun, from_lib: "eqc/include/eqc_mocking_api.hrl")

Compile deps using mix compile. Everything works now.

Writing property tests

Check test/elixir_quickcheck_example.exs. This test was used on ElixirConf EU 2015: https://www.youtube.com/watch?v=nbpZRm9gl50

Run mix test and... it fails:

** (CompileError) test/elixir_quickcheck_example_test.exs:8: function equals/2 undefined

After checking :eqc_ex sources, change equals/2 into ensure a == b:

# equals(:lists.seq(m, n), Enum.to_list(m..n))
ensure :lists.seq(m, n) == Enum.to_list(m..n)

Run mix test and it works:

$ mix test
....Failed! After 5 tests.
{1,0}
not ensured: [] == [1, 0]
Shrinking x(0 times)
{1,0}
not ensured: [] == [1, 0]


  1) test Property Erlang sequence (ElixirQuickcheckExampleTest)
     test/elixir_quickcheck_example_test.exs:6
     forall({m, n} <- {int, int}) do
       ensure(:lists.seq(m, n) == Enum.to_list(m .. n))
     end
     Failed for {1, 0}