Testing: Add tests for new MachO.open

Ensure that MachO.open raises all expected exceptions.

Author: woodruffw

test/test_open.rb

@@ -5,6 +5,32 @@
 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
+
+  # MachO.open has slightly looser qualifications for truncation than
+  # either MachOFile.new or FatFile.new - it just makes sure that there are
+  # enough magic bytes to read, and lets the actual parser raise a
+  # TruncationError later on if required.
+  def test_truncated_file
+    tempfile_with_data("truncated_file", "\x00\x00") do |truncated_file|
+      assert_raises MachO::TruncatedFileError do
+        MachO.open(truncated_file.path)
+      end
+    end
+  end
+
+  def test_bad_magic
+    tempfile_with_data("junk_file", "\xFF\xFF\xFF\xFF") do |junk_file|
+      assert_raises MachO::MagicError do
+        MachO.open(junk_file.path)
+      end
+    end
+  end
+
   def test_open
     file = MachO.open("test/bin/libhello.dylib")