Testing: Add tests for new MachO.open

Ensure that MachO.open raises all expected exceptions.

Author: woodruffw

test/test_open.rb

@@ -5,6 +5,12 @@
 class MachOOpenTest < Minitest::Test
   include Helpers
 
+  def test_nonexistent_file
+    assert_raises ArgumentError do
+      MachO.open("/this/is/a/file/that/cannot/possibly/exist")
+    end
+  end
+
   def test_open
     file = MachO.open("test/bin/libhello.dylib")