Hegel.ExUnit (hegel_elixir v0.1.0)

ExUnit integration for Hegel properties.

use Hegel.ExUnit sets up an ExUnit case, imports Hegel's generators, and provides the property and check all macros.

The DSL follows StreamData's property and check all syntax:

property "reversing twice preserves a list" do
  check all values <- list_of(integer()) do
    assert values |> Enum.reverse() |> Enum.reverse() == values
  end
end

Hegel evaluates generator clauses from left to right, so later generators can use earlier draws. A pattern mismatch or a false clause rejects the example as an assumption.

Summary

Functions

__using__(opts)

Sets up a module as an ExUnit case with Hegel's property-testing DSL.

check(arg)

Checks a property against values drawn from one or more generators.

property(message)

Defines a pending property.

property(message, context \\ quote do _ end, contents)

Defines an ExUnit property.

Functions

using(opts)

(macro)

Sets up a module as an ExUnit case with Hegel's property-testing DSL.

Hegel passes all options to ExUnit.Case unless the module already uses it.

check(arg)

(macro)

Checks a property against values drawn from one or more generators.

Generator clauses use <-. Later generators and clauses may use bindings introduced by earlier clauses:

check all values <- list_of(integer()),
          index <- integer(min: 0, max: max(length(values) - 1, 0)),
          values != [],
          selected = Enum.at(values, index),
          test_cases: 250 do
  assert selected in values
end

A pattern mismatch or a false clause rejects the current test case through Hegel.assume/3. Hegel passes the trailing keyword options to Hegel.check/2.

check all derives :database_key from the caller module and property function when you omit it, so stored counterexamples retain the same key across runs.

property(message)

(macro)

Defines a pending property.

The ExUnit test receives :property and :not_implemented tags and fails with "Not implemented".

property(message, context \\ quote do _ end, contents)

(macro)

Defines an ExUnit property.

Pass an optional context pattern as you would to ExUnit.Case.test/3:

property "uses setup data", %{account: account} do
  check all suffix <- text() do
    assert is_binary(account.name <> suffix)
  end
end