diff --git a/gabbi/handlers.py b/gabbi/handlers.py
index f754d94..d39a987 100644
--- a/gabbi/handlers.py
+++ b/gabbi/handlers.py
@@ -120,6 +120,8 @@ class HeadersResponseHandler(ResponseHandler):
     test_key_value = {}
 
     def action(self, test, header, value):
+        header = header.lower()  # case-insensitive comparison
+
         response = test.response
         header_value = test.replace_template(value)
 

case-insensitive headers
As far as I can tell, gabbi enforces lowercase headers:

```yaml
response_headers:
    content-type: text/html; charset=utf-8
```

```
... ✓ front page returns HTML
```

vs.

```yaml
response_headers:
    Content-Type: text/html; charset=utf-8
```

```
... E front page returns HTML

ERROR: front page returns HTML
	 "'Content-Type' header not available in response keys: dict_keys(['server', 'content-type', 'access-control-allow-origin', 'date', 'access-control-allow-credentials', 'connection', 'content-location', 'content-length', 'status'])"
```

From my perspective, the second version is more readable - so it would be nice if header name comparisons were case-insensitive.

diff --git a/gabbi/tests/test_handlers.py b/gabbi/tests/test_handlers.py
index b18e8ec..b647e80 100644
--- a/gabbi/tests/test_handlers.py
+++ b/gabbi/tests/test_handlers.py
@@ -94,10 +94,16 @@ class HandlersTest(unittest.TestCase):
 
     def test_response_headers(self):
         handler = handlers.HeadersResponseHandler(self.test_class)
+        self.test.response = {'content-type': 'text/plain'}
+
         self.test.test_data = {'response_headers': {
             'content-type': 'text/plain',
         }}
-        self.test.response = {'content-type': 'text/plain'}
+        self._assert_handler(handler)
+
+        self.test.test_data = {'response_headers': {
+            'Content-Type': 'text/plain',
+        }}
         self._assert_handler(handler)
 
     def test_response_headers_regex(self):

pip install -e .
parse_log_pytest
requirements.txt
tox pytest
pip install tox
3.4
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
attrs==22.2.0
certifi==2021.5.30
decorator==5.1.1
distlib==0.3.9
filelock==3.4.1
fixtures==4.0.1
-e git+https://github.com/cdent/gabbi.git@f2a32ad31bc205580834f009f05586a533f390f7#egg=gabbi
httplib2==0.22.0
importlib-metadata==4.8.3
importlib-resources==5.4.0
iniconfig==1.1.1
jsonpath-rw==1.4.0
packaging==21.3
pbr==6.1.1
platformdirs==2.4.0
pluggy==1.0.0
ply==3.11
py==1.11.0
pyparsing==3.1.4
pytest==7.0.1
PyYAML==6.0.1
six==1.17.0
testtools==2.6.0
toml==0.10.2
tomli==1.2.3
tox==3.28.0
typing_extensions==4.1.1
virtualenv==20.17.1
wsgi_intercept==1.13.1
zipp==3.6.0

name: gabbi
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - attrs==22.2.0
      - decorator==5.1.1
      - distlib==0.3.9
      - filelock==3.4.1
      - fixtures==4.0.1
      - httplib2==0.22.0
      - importlib-metadata==4.8.3
      - importlib-resources==5.4.0
      - iniconfig==1.1.1
      - jsonpath-rw==1.4.0
      - packaging==21.3
      - pbr==6.1.1
      - platformdirs==2.4.0
      - pluggy==1.0.0
      - ply==3.11
      - py==1.11.0
      - pyparsing==3.1.4
      - pytest==7.0.1
      - pyyaml==6.0.1
      - six==1.17.0
      - testtools==2.6.0
      - toml==0.10.2
      - tomli==1.2.3
      - tox==3.28.0
      - typing-extensions==4.1.1
      - virtualenv==20.17.1
      - wsgi-intercept==1.13.1
      - zipp==3.6.0
prefix: /opt/conda/envs/gabbi

gabbi/tests/test_handlers.py::HandlersTest::test_response_headers
gabbi/tests/test_handlers.py::HandlersTest::test_response_headers_fail_data gabbi/tests/test_handlers.py::HandlersTest::test_response_headers_fail_header gabbi/tests/test_handlers.py::HandlersTest::test_response_headers_regex gabbi/tests/test_handlers.py::HandlersTest::test_response_json_paths gabbi/tests/test_handlers.py::HandlersTest::test_response_json_paths_fail_data gabbi/tests/test_handlers.py::HandlersTest::test_response_json_paths_fail_path gabbi/tests/test_handlers.py::HandlersTest::test_response_strings gabbi/tests/test_handlers.py::HandlersTest::test_response_strings_fail
gabbi/handlers.py
gabbi/handlers.py