Add test for multiple language support

This test does not require any additional tesseract language backends to be
installed, but might fail if tesseract changes its error messages in the
future.

Author: Michal Barla

test/unit/test_extract_text.rb

@@ -40,7 +40,7 @@ def test_ocr_extraction
 
   def test_ocr_extraction_in_mock_language
     exception = assert_raise(Docsplit::ExtractionFailed) {Docsplit.extract_text('test/fixtures/corrosion.pdf', :pages => 'all', :output => OUTPUT, :language => "mock")}
-    assert(exception.message.match("mock.traineddata"))
+    assert exception.message.match("tessdata/mock"), "Expected problem with loading data for language 'mock'"
   end
 
   def test_password_protected