nose can't really handle external tests so looking into py.test instead

Specifically it trips over the need to reimport ocrmypdf.main.  That in
turn raises questions about whether to make that function into an
external script that imports ocrmypdf... or something else.  Would be
possible with a loop that manipulates sys_argv and then reloads
ocrmypdf.main; might need that anyway.

tests/test_main.py

@@ -6,7 +6,10 @@ import os
 import shutil
 from contextlib import suppress
 import sys
-from unittest.mock import patch
+from unittest.mock import patch, create_autospec
+from nose import with_setup
+from nose.tools import raises
+
 
 if sys.version_info.major < 3:
     print("Requires Python 3.4+")
@@ -37,7 +40,7 @@ def run_ocrmypdf_sh(input_file, output_file, *args):
 
 def check_ocrmypdf_sh(input_basename, output_basename, *args):
     input_file = os.path.join(TEST_RESOURCES, input_basename)
-    output_file = os.path.join(TEST_OUTPUT, output_basename or input_basename)
+    output_file = os.path.join(TEST_OUTPUT, output_basename)
 
     sh, _, err = run_ocrmypdf_sh(input_file, output_file, *args)
     assert sh.returncode == 0, err
@@ -47,23 +50,20 @@ def check_ocrmypdf_sh(input_basename, output_basename, *args):
 
 def run_ocrmypdf(input_basename, output_basename, *args):
     input_file = os.path.join(TEST_RESOURCES, input_basename)
-    output_file = os.path.join(TEST_OUTPUT, output_basename or input_basename)
+    output_file = os.path.join(TEST_OUTPUT, output_basename)
 
     sys_argv = list(args) + [input_file, output_file]
     with patch.object(sys, 'argv', sys_argv):
-        try:
-            import ocrmypdf.main
-            ocrmypdf.main.run_pipeline()
-        except SystemExit as e:
-            assert e.code == 0
+        import ocrmypdf.main
+        ocrmypdf.main.run_pipeline()
     return output_file
 
 
-def test_quick():
+def xtest_quick():
     check_ocrmypdf_sh('c02-22.pdf', 'test_quick.pdf')
 
 
-def test_deskew():
+def xtest_deskew():
     # Run with deskew
     deskewed_pdf = run_ocrmypdf('skew.pdf', 'test_deskew.pdf', '-d')
 
@@ -92,7 +92,7 @@ def test_deskew():
     assert -0.5 < skew_angle < 0.5, "Deskewing failed"
 
 
-def test_clean():
+def xtest_clean():
     check_ocrmypdf_sh('skew.pdf', 'test_clean.pdf', '-c')
 
 
@@ -116,9 +116,10 @@ def test_metadata():
     assert pdfinfo.get('Keywords', '') == ''
 
 
-def test_oversample():
+def check_oversample(renderer):
     oversampled_pdf = run_ocrmypdf(
-        'skew.pdf', 'test-oversample.pdf', '--oversample', '300')
+        'skew.pdf', 'test_oversample_%s.pdf' % renderer, '--oversample', '300',
+        '--pdf-renderer', renderer)
 
     from ocrmypdf.pageinfo import pdf_get_all_pageinfo
 
@@ -126,3 +127,19 @@ def test_oversample():
 
     print(pdfinfo[0]['xres'])
     assert abs(pdfinfo[0]['xres'] - 300) < 1
+
+
+def test_oversample():
+    yield check_oversample, 'hocr'
+    yield check_oversample, 'tesseract'
+
+
+@raises(SystemExit)
+def test_repeat_ocr():
+    run_ocrmypdf('graph_ocred.pdf', 'wontwork.pdf')
+
+
+def test_force_ocr():
+    run_ocrmypdf('graph_ocred.pdf', 'test_force.pdf')
+
+