improve code coverage in a few places

src/flake8/processor.py

@@ -446,8 +446,6 @@ def log_token(log: logging.Logger, token: _Token) -> None:
     )
 
 
-# NOTE(sigmavirus24): This was taken wholesale from
-# https://github.com/PyCQA/pycodestyle
 def expand_indent(line: str) -> int:
     r"""Return the amount of indentation.
 
@@ -462,17 +460,7 @@ def expand_indent(line: str) -> int:
     >>> expand_indent('        \t')
     16
     """
-    if "\t" not in line:
-        return len(line) - len(line.lstrip())
-    result = 0
-    for char in line:
-        if char == "\t":
-            result = result // 8 * 8 + 8
-        elif char == " ":
-            result += 1
-        else:
-            break
-    return result
+    return len(line.expandtabs(8))
 
 
 # NOTE(sigmavirus24): This was taken wholesale from

src/flake8/utils.py

@@ -231,9 +231,7 @@ def parse_unified_diff(diff: Optional[str] = None) -> Dict[str, Set[int]]:
     parsed_paths: Dict[str, Set[int]] = collections.defaultdict(set)
     for line in diff.splitlines():
         if number_of_rows:
-            # NOTE(sigmavirus24): Below we use a slice because stdin may be
-            # bytes instead of text on Python 3.
-            if line[:1] != "-":
+            if not line or line[0] != "-":
                 number_of_rows -= 1
             # We're in the part of the diff that has lines starting with +, -,
             # and ' ' to show context and the changes made. We skip these
@@ -317,7 +315,6 @@ def _default_predicate(*args: str) -> bool:
 def filenames_from(
     arg: str, predicate: Optional[Callable[[str], bool]] = None
 ) -> Generator[str, None, None]:
-    # noqa: E501
     """Generate filenames from an argument.
 
     :param str arg: