test: Cut not_equal

tests/prolog/builtins/ControlOperatorsTests.kt

@@ -17,6 +17,8 @@ class ControlOperatorsTests {
         Program.clear()
     }
 
+    // See also: https://stackoverflow.com/a/23292126
+
     @Test
     fun `simple cut program`() {
         // First an example without cut
@@ -149,6 +151,32 @@ class ControlOperatorsTests {
         assertEquals(1, result.size, "Expected 1 result")
     }
 
+    @Test
+    fun `not_equal cut test`() {
+        Program.load(
+            listOf(
+                Rule(
+                    CompoundTerm(Atom("not_equal"), listOf(Variable("X"), Variable("Y"))),
+                    Conjunction(
+                        Unify(Variable("X"), Variable("Y")),
+                        Conjunction(Cut(), Fail)
+                    )
+                ),
+                Fact(CompoundTerm(Atom("not_equal"), listOf(Variable("_1"), Variable("_2"))))
+            )
+        )
+
+        var goal = CompoundTerm(Atom("not_equal"), listOf(Integer(1), Integer(1)))
+        var result = Program.query(goal).toList()
+
+        assertTrue(result.none(), "Expected no results")
+
+        goal = CompoundTerm(Atom("not_equal"), listOf(Integer(1), Integer(2)))
+        result = Program.query(goal).toList()
+
+        assertEquals(1, result.size, "Expected 1 result")
+    }
+
     @Test
     fun not_atom() {
         val success = Fact(Atom("a"))