fix-whitespace: Added test for custom charsets

pre_commit_hooks/trailing_whitespace_fixer.py

diff --git a/pre_commit_hooks/trailing_whitespace_fixer.py b/pre_commit_hooks/trailing_whitespace_fixer.py
index 88b3f93..70ab382 100644
--- a/pre_commit_hooks/trailing_whitespace_fixer.py
+++ b/pre_commit_hooks/trailing_whitespace_fixer.py
@@ -29,13 +29,15 @@
     # type: (bytes, bool, Optional[bytes]) -> bytes
     if line[-2:] == b'\r\n':
         eol = b'\r\n'
+        line = line[:-2]
     elif line[-1:] == b'\n':
         eol = b'\n'
+        line = line[:-1]
     else:
         eol = b''
     # preserve trailing two-space for non-blank lines in markdown files
-    if is_markdown and (not line.isspace()) and line.endswith(b'  ' + eol):
-        return line.rstrip(chars_to_strip) + b'  ' + eol
+    if is_markdown and (not line.isspace()) and line.endswith(b'  '):
+        return line[:-2].rstrip(chars_to_strip) + b'  ' + eol
     return line.rstrip(chars_to_strip) + eol
 
 

tests/trailing_whitespace_fixer_test.py

diff --git a/tests/trailing_whitespace_fixer_test.py b/tests/trailing_whitespace_fixer_test.py
index 82c9b6d..ec4c918 100644
--- a/tests/trailing_whitespace_fixer_test.py
+++ b/tests/trailing_whitespace_fixer_test.py
@@ -78,3 +78,19 @@
     ret = main([path.strpath])
     assert ret == 1
     assert path.size() == (len(non_utf8_bytes_content) - 1)
+
+
+def test_custom_charset_change(tmpdir):
+    # strip spaces only, no tabs
+    path = tmpdir.join('file.txt')
+    path.write('\ta \t \n')
+    ret = main([path.strpath, '--chars', ' '])
+    assert ret == 1
+    assert path.read() == '\ta \t\n'
+
+
+def test_custom_charset_no_change(tmpdir):
+    path = tmpdir.join('file.txt')
+    path.write('\ta \t\n')
+    ret = main([path.strpath, '--chars', ' '])
+    assert ret == 0