alter file with new line even if no other content is changed

pre_commit_hooks/requirements_txt_fixer.py

diff --git a/pre_commit_hooks/requirements_txt_fixer.py b/pre_commit_hooks/requirements_txt_fixer.py
index 55744c6..1691d80 100644
--- a/pre_commit_hooks/requirements_txt_fixer.py
+++ b/pre_commit_hooks/requirements_txt_fixer.py
@@ -43,13 +43,13 @@
     before = list(f)  # type: List[bytes]
     after = []  # type: List[bytes]
 
+    before_string = b''.join(before)
+
     # adds new line in case one is missing
     # AND a change to the requirements file is needed regardless:
     if before and not before[-1].endswith(b'\n'):
         before[-1] += b'\n'
 
-    before_string = b''.join(before)
-
     # If the file is empty (i.e. only whitespace/newlines) exit early
     if before_string.strip() == b'':
         return PASS
@@ -99,7 +99,7 @@
 
     after_string = b''.join(after)
 
-    if before_string.rstrip() == after_string.rstrip():
+    if before_string == after_string:
         return PASS
     else:
         f.seek(0)

tests/requirements_txt_fixer_test.py

diff --git a/tests/requirements_txt_fixer_test.py b/tests/requirements_txt_fixer_test.py
index 7c74ffc..2e2eab6 100644
--- a/tests/requirements_txt_fixer_test.py
+++ b/tests/requirements_txt_fixer_test.py
@@ -17,7 +17,7 @@
         (b'bar\nfoo\n', PASS, b'bar\nfoo\n'),
         (b'a\nc\nb\n', FAIL, b'a\nb\nc\n'),
         (b'a\nc\nb', FAIL, b'a\nb\nc\n'),
-        (b'a\nb\nc', PASS, b'a\nb\nc'),
+        (b'a\nb\nc', FAIL, b'a\nb\nc\n'),
         (
             b'#comment1\nfoo\n#comment2\nbar\n',
             FAIL,