StreamData is an Elixir library for data generation and property-based testing.
Read the announcement on the Elixir website.
Add stream_data
to your list of dependencies:
defp deps() do
[{:stream_data, "~> 0.5", only: :test}]
end
and run mix deps.get
. StreamData is usually added only to the :test
environment since it's used in tests and test data generation.
To also import StreamData's formatter configuration, add the :dev
environment as well as :test
for stream_data
and add :stream_data
to your .formatter.exs
:
[
import_deps: [:stream_data]
]
The documentation is available online.
StreamData is made of two main components: data generation and property-based testing. The StreamData
module provides tools to work with data generation. The ExUnitProperties
module takes care of the property-based testing functionality.
All data generation functionality is provided in the StreamData
module. StreamData
provides "generators" and functions to combine those generators and create new ones. Since generators implement the Enumerable
protocol, it's easy to use them as infinite streams of data:
StreamData.integer() |> Stream.map(&abs/1) |> Enum.take(3)
#=> [1, 0, 2]
StreamData
provides all the necessary tools to create arbitrarily complex custom generators:
require ExUnitProperties
domains = [
"gmail.com",
"hotmail.com",
"yahoo.com",
]
email_generator =
ExUnitProperties.gen all name <- StreamData.string(:alphanumeric),
name != "",
domain <- StreamData.member_of(domains) do
name <> "@" <> domain
end
Enum.take(StreamData.resize(email_generator, 20), 2)
#=> ["[email protected]", "[email protected]"]
Property testing aims at randomizing test data in order to make tests more robust. Instead of writing a bunch of inputs and expected outputs by hand, with property-based testing we write a property of our code that should hold for a set of data, and then we generated data in this set to verify that property. To generate this data, we can use the above-mentioned StreamData
module.
use ExUnitProperties
property "bin1 <> bin2 always starts with bin1" do
check all bin1 <- binary(),
bin2 <- binary() do
assert String.starts_with?(bin1 <> bin2, bin1)
end
end
To know more about property-based testing, read the ExUnitProperties
documentation. Another great resource about property-based testing in Erlang (but with most ideas that apply to Elixir as well) is Fred Hebert's website propertesting.com.
The property-based testing side of this library is heavily inspired by the original QuickCheck paper (which targeted Haskell) as well as Clojure's take on property-based testing, test.check.
There are a handful of property-based testing frameworks for the BEAM ecosystem (Erlang, Elixir, and so on). For Elixir, the main alternative to StreamData is PropCheck. PropCheck is a wrapper around PropEr, which is a property-based testing framework for Erlang. There are a few fundamental differences between StreamData and PropEr. They are listed below to help you choose between the two.
PropEr (via PropCheck):
-
It provides stateful property-based testing. If you need to test a system with state by building a model of the system to test against, you'll have to go with PropCheck since StreamData doesn't support this yet.
-
It can store counter-examples: StreamData doesn't support storing counter-examples in a file (you have to reuse the seed that caused the failure in order to reproduce it).
StreamData:
-
Provides functionality for generating data as the base for property-based testing. StreamData generators can be used outside of property-based testing as normal Elixir streams that produce random data.
-
It is native to Elixir. It's written entirely in Elixir and has an idiomatic Elixir API (for example, all generators are Elixir enumerables).
Copyright 2017 Andrea Leopardi and José Valim
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.