Add ((1 x) (2 y) (x) (y 8)) test case

src/test/scala/pl/edu/agh/kis/eis/ndl/KnowledgeBaseSpec.scala

@@ -126,6 +126,24 @@ class KnowledgeBaseSpec extends FlatSpec with Matchers {
     kb.queryAll(Functor(x), Functor(x, Const(1))).toSeq should be(empty)
   }
 
+  "Query ((1 x) (2 y) (x) (y 8))" should "be unified" in {
+    val kb = new KnowledgeBase[Int](Set(
+      Tuple1(2), Tuple1(3), Tuple1(4), (1, 3), (2, 5), Tuple1(4), (2, 2), (2, 8), (7, 8), Tuple1(7),
+      (1, 4), (1, 8)
+    ))
+
+    val x = Variable[Int]("x")
+    val y = Variable[Int]("y")
+
+    kb.queryAll(
+      Functor(x), Functor(Const(1), x), Functor(Const(2), y), Functor(y, Const(8))
+    ).toSeq should
+      contain theSameElementsAs Seq(
+      Set(Variable("x", 3), Variable("y", 2)),
+      Set(Variable("x", 4), Variable("y", 2))
+    )
+  }
+
   "Query ((x) (y) (x y))" should "be unified" ignore {
     val kb: KnowledgeBase[Int] = new KnowledgeBase[Int](Set(
       Tuple1(2), Tuple1(8), (2, 8), // solution: x = 2, y = 8