test: such that constraints [Closes parroty#14]

lib/excheck/statement.ex

@@ -35,8 +35,8 @@ defmodule ExCheck.Statement do
   end
 
   @doc """
-  Verify property and return the result as true/faluse value.
-  It corresonds to triq#check_forall method.
+  Verify property and return the result as true/false value.
+  It corresponds to triq#check_forall method.
   """
   def verify_property({:"prop:forall", domain, _syntax, fun, _body}) do
     iterations = Application.get_env(:excheck, :number_iterations, 100)

test/such_that_test.exs

@@ -0,0 +1,24 @@
+defmodule ExCheck.SuchThatTest do
+  use ExUnit.Case
+  use ExCheck
+
+  # https://github.com/parroty/excheck/issues/14
+  property :stj_such_that_constraints do
+    for_all {s, t, j} in such_that({s_, t_, j_} in {int(), int(), int()} when s_ < j_ and j_ < t_) do
+      assert j > s, inspect([s, j, t])
+      assert j < t, inspect([s, j, t])
+    end
+  end
+
+  defp gen_sjt,
+    do:
+      [int(), pos_integer(), pos_integer()]
+      |> bind(fn [s, dj, dt] -> {s, s + dj, s + dj + dt} end)
+
+  property :sjt_bind do
+    for_all {s, j, t} in gen_sjt() do
+      assert j > s, inspect([s, j, t])
+      assert j < t, inspect([s, j, t])
+    end
+  end
+end