add haskell test

Author: mlysle

tests/treewalker/haskell_spec.lua

@@ -27,6 +27,14 @@ describe("In a haskell file: ", function()
     tw.move_out()
     h.assert_cursor_at(19, 1)
   end)
+
+  it("swaparound behavior works", function()
+	  vim.fn.cursor(40,15) -- (|node1, node2)
+    tw.swap_left()
+    assert.same("  printEvens [9, 3, 5, 7, 1]", lines.get_line(40))
+    tw.swap_right()
+    assert.same("  printEvens [1, 3, 5, 7, 9]", lines.get_line(40))
+  end)
 end)