Add optional extension keyword argument to set_cover()

Previously, set_cover() would rely on the Python standard module
`imghdr` to determine the type of the specified cover image file.
Unfortunately, imghdr does not support SVG, so set_cover() could
not handle that type (which is permitted by the EPUB spec).

Detecting SVG files programmatically is nontrivial, and is generally
considered to require parsing the file source.

Instead, simply provide an option for the client to specify the file
type with the new keyword argument.

.travis.yml

@@ -7,6 +7,7 @@ install:
 - pip install jinja2
 - pip install -e .
 - pip install 'pytest-cov>=2.4.0,<2.6'
+- pip install pytest-mock
 - pip install python-coveralls
 script: py.test --cov=mkepub/ --cov-report=term-missing
 after_success:

mkepub/mkepub.py

@@ -108,9 +108,11 @@ def add_font(self, name, data):
         self.fonts.append(name)
         self._add_file(pathlib.Path('fonts') / name, data)
 
-    def set_cover(self, data):
+    def set_cover(self, data, extension=None):
         """Set the cover image to the given data."""
-        self._cover = 'cover.' + imghdr.what(None, h=data)
+        if not extension:
+            extension = imghdr.what(None, h=data)
+        self._cover = 'cover.' + extension
         self._add_file(pathlib.Path('covers') / self._cover, data)
         self._write('cover.xhtml', 'EPUB/cover.xhtml', cover=self._cover)
 

mkepub/tests/test_mkepub.py

@@ -130,11 +130,47 @@ def test_book_with_dcterms():
     ]
     assert_has_contents(book, 'EPUB/package.opf', expected_strings)
 
-    
+
 def test_mediatype():
     assert mkepub.mkepub.mediatype('file.png') == 'image/png'
     assert mkepub.mkepub.mediatype('file.jpg') == 'image/jpeg'
     assert mkepub.mkepub.mediatype('file.jpeg') == 'image/jpeg'
     assert mkepub.mkepub.mediatype('file.gif') == 'image/gif'
     assert mkepub.mkepub.mediatype('file.svg') == 'image/svg+xml'
 
+
+class TestSetCover:
+    def test_set_cover_auto(self, mocker):
+        mocker.patch("mkepub.Book._add_file")
+        mocker.patch("mkepub.Book._write")
+
+        book = mkepub.Book('SetCover')
+
+        with open('mkepub/tests/cover.jpg', 'rb') as file:
+            data = file.read()
+        book.set_cover(data)
+        mkepub.Book._add_file.assert_called_with(pathlib.PosixPath('covers/cover.jpeg'), data)
+        mkepub.Book._write.assert_called_with(mocker.ANY, mocker.ANY, cover='cover.jpeg')
+
+    def test_set_cover_override(self, mocker):
+        mocker.patch("mkepub.Book._add_file")
+        mocker.patch("mkepub.Book._write")
+
+        book = mkepub.Book('SetCover')
+
+        with open('mkepub/tests/cover.jpg', 'rb') as file:
+            data = file.read()
+        book.set_cover(data, extension='png')
+        mkepub.Book._add_file.assert_called_with(pathlib.PosixPath('covers/cover.png'), data)
+        mkepub.Book._write.assert_called_with(mocker.ANY, mocker.ANY, cover='cover.png')
+
+    def test_set_cover_undetectable(self, mocker):
+        mocker.patch("mkepub.Book._add_file")
+        mocker.patch("mkepub.Book._write")
+
+        book = mkepub.Book('SetCover')
+
+        data = b'<svg></svg>'
+        book.set_cover(data, extension='svg')
+        mkepub.Book._add_file.assert_called_with(pathlib.PosixPath('covers/cover.svg'), data)
+        mkepub.Book._write.assert_called_with(mocker.ANY, mocker.ANY, cover='cover.svg')

setup.py

@@ -22,6 +22,6 @@
         'Programming Language :: Python :: 3.5'],
     packages=['mkepub'],
     package_data={'mkepub': ['templates/*']},
-    tests_require=['epubcheck', 'pytest', 'pytest-cov', 'python-coveralls'],
+    tests_require=['epubcheck', 'pytest', 'pytest-cov', 'pytest-mock', 'python-coveralls'],
     install_requires=['jinja2'],
 )