Prevent use of —pdf-renderer tess4 on tesseract 3

ocrmypdf/__main__.py

@@ -333,6 +333,10 @@ def check_options_advanced(options, log):
     if options.tesseract_oem and not tesseract.v4():
         log.warning(
             "--tesseract-oem requires Tesseract 4.x -- argument ignored")
+    if options.pdf_renderer == 'tess4' and not tesseract.has_textonly_pdf():
+        raise MissingDependencyError(
+            "--pdf-renderer tess4 requires Tesseract 4.x "
+            "commit 3d9fb3b or later")
 
 
 def check_options(options, log):

tests/test_tess3.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+# © 2017 James R. Barlow: github.com/jbarlow83
+
+import pytest
+from ocrmypdf.exceptions import ExitCode
+from ocrmypdf.exec import tesseract
+
+
+# Skip all tests in this file if not tesseract 3
+pytestmark = pytest.mark.skipif(tesseract.v4(),
+                                reason="tesseract 3.x required")
+
+
+def test_textonly_pdf_on_tess3(resources, no_outpdf):
+    p, _, _ = pytest.helpers.run_ocrmypdf(
+        resources / 'linn.pdf',
+        no_outpdf, '--pdf-renderer', 'tess4')
+
+    assert p.returncode == ExitCode.missing_dependency
+
+
+def test_oem_on_tess3(resources, no_outpdf):
+    p, _, err = pytest.helpers.run_ocrmypdf(
+        resources / 'aspect.pdf',
+        no_outpdf, '--tesseract-oem', '1')
+
+    assert p.returncode == ExitCode.ok
+    assert 'argument ignored' in err

tests/test_tess4.py

@@ -1,17 +1,8 @@
 #!/usr/bin/env python3
 # © 2017 James R. Barlow: github.com/jbarlow83
 
-from subprocess import Popen, PIPE, check_output, check_call, DEVNULL
-import os
-import shutil
-from contextlib import suppress
-import sys
 import pytest
-from ocrmypdf.pageinfo import pdf_get_all_pageinfo
-import PyPDF2 as pypdf
 from ocrmypdf.exceptions import ExitCode
-from ocrmypdf import leptonica
-from ocrmypdf.pdfa import file_claims_pdfa
 from ocrmypdf.exec import tesseract