ExUnit helpers for asserting that Bond contract violations are raised.

Each macro wraps the given expression in an ExUnit.Assertions.assert_raise/2 that expects the matching Bond.PreconditionError / Bond.PostconditionError / Bond.CheckError, and optionally checks fields on the raised exception against a keyword of expected values.

Field expectations may be exact values or Regex patterns. Regexes are matched against the string form of the field (the exception's :expression field is a string; the :file field is also a string). Any other expected value must be equal (via ==) to the field's value.

Usage

defmodule MyAppTest do
  use ExUnit.Case
  use Bond.Test

  alias MyApp.Math

  test "rejects negative input" do
    assert_precondition_violation(Math.sqrt(-1), label: :non_negative_x)
  end

  test "rejects non-numeric input with a regex on the expression" do
    assert_precondition_violation(Math.sqrt("NaN"),
      label: :numeric_x,
      expression: ~r/is_number/
    )
  end

  test "postcondition violation when result is not a float" do
    assert_postcondition_violation(Math.sqrt(2, fn _ -> 10 end),
      module: MyApp.Math,
      function: {:sqrt, 2}
    )
  end
end

Each helper returns the raised exception struct so further assertions can be made on it:

error = assert_precondition_violation(Math.sqrt(-1))
assert error.binding[:x] == -1