chore: Refactor checksum comparisons

- Use a DRY method instead.
- ENV test changed from 2048-bit to 3072-bit to avoid confusion in a future test that should not be mixed up accidentally with 2048-bit elsewhere.
- Custom DH file test comparison changed to match other comparisons for equality against the expected DH param content.
- Related comments revised, additional comment for context added by the test definition.
- Minor white-space adjustments.

test/test_ssl/test_dhparam.py

@@ -101,6 +101,13 @@ def cannot_negotiate_dhe_ciphersuite(sut_container):
     assert "X25519" in r3
 
 
+def should_be_equivalent_content(sut_container, expected, actual):
+    expected_checksum = sut_container.exec_run(f"md5sum {expected}").output.split()[0]
+    actual_checksum = sut_container.exec_run(f"md5sum {actual}").output.split()[0]
+
+    assert expected_checksum == actual_checksum
+
+
 # Parse array of container ENV, splitting at the `=` and returning the value, otherwise `None`
 def get_env(sut_container, var):
   env = sut_container.attrs['Config']['Env']
@@ -125,14 +132,17 @@ def test_default_dhparam_is_ffdhe4096(docker_compose):
 
     assert_log_contains("Setting up DH Parameters..", container_name)
 
-    # Make sure the dhparam file used is the default ffdhe4096.pem:
-    default_checksum = sut_container.exec_run("md5sum /app/dhparam/ffdhe4096.pem").output.split()
-    current_checksum = sut_container.exec_run("md5sum /etc/nginx/dhparam/dhparam.pem").output.split()
-    assert default_checksum[0] == current_checksum[0]
+    # `dhparam.pem` contents should match the default (ffdhe4096.pem):
+    should_be_equivalent_content(
+        sut_container,
+        "/app/dhparam/ffdhe4096.pem",
+        "/etc/nginx/dhparam/dhparam.pem"
+    )
 
     can_negotiate_dhe_ciphersuite(sut_container)
 
 
+# Overrides default DH group via ENV `DHPARAM_BITS=3072`:
 def test_can_change_dhparam_group(docker_compose):
     container_name="dh-env"
     sut_container = docker_client.containers.get(container_name)
@@ -140,10 +150,12 @@ def test_can_change_dhparam_group(docker_compose):
 
     assert_log_contains("Setting up DH Parameters..", container_name)
 
-    # Make sure the dhparam file used is ffdhe2048.pem, not the default (ffdhe4096.pem):
-    default_checksum = sut_container.exec_run("md5sum /app/dhparam/ffdhe2048.pem").output.split()
-    current_checksum = sut_container.exec_run("md5sum /etc/nginx/dhparam/dhparam.pem").output.split()
-    assert default_checksum[0] == current_checksum[0]
+    # `dhparam.pem` contents should not match the default (ffdhe4096.pem):
+    should_be_equivalent_content(
+        sut_container,
+        "/app/dhparam/ffdhe3072.pem",
+        "/etc/nginx/dhparam/dhparam.pem"
+    )
 
     can_negotiate_dhe_ciphersuite(sut_container)
 
@@ -162,6 +174,7 @@ def test_fail_if_dhparam_group_not_supported(docker_compose):
     )
 
 
+# Overrides default DH group by providing a custom `/etc/nginx/dhparam/dhparam.pem`:
 def test_custom_dhparam_is_supported(docker_compose):
     container_name="dh-file"
     sut_container = docker_client.containers.get(container_name)
@@ -172,10 +185,12 @@ def test_custom_dhparam_is_supported(docker_compose):
         container_name
     )
 
-    # Make sure the dhparam file used is not the default (ffdhe4096.pem):
-    default_checksum = sut_container.exec_run("md5sum /app/dhparam/ffdhe4096.pem").output.split()
-    current_checksum = sut_container.exec_run("md5sum /etc/nginx/dhparam/dhparam.pem").output.split()
-    assert default_checksum[0] != current_checksum[0]
+    # `dhparam.pem` contents should not match the default (ffdhe4096.pem):
+    should_be_equivalent_content(
+        sut_container,
+        "/app/dhparam/ffdhe3072.pem",
+        "/etc/nginx/dhparam/dhparam.pem"
+    )
 
     can_negotiate_dhe_ciphersuite(sut_container)
 
@@ -189,6 +204,7 @@ def test_can_skip_dhparam(docker_compose):
 
     cannot_negotiate_dhe_ciphersuite(sut_container)
 
+
 def test_can_skip_dhparam_backward_compatibility(docker_compose):
     container_name="dh-skip-backward"
     sut_container = docker_client.containers.get(container_name)

test/test_ssl/test_dhparam.yml

@@ -19,7 +19,7 @@ with_default_group:
 with_alternative_group:
   container_name: dh-env
   environment:
-    - DHPARAM_BITS=2048
+    - DHPARAM_BITS=3072
   image: *img-nginxproxy
   volumes: *vols-common
 
@@ -33,7 +33,7 @@ with_invalid_group:
 with_custom_file:
   container_name: dh-file
   image: *img-nginxproxy
-  volumes: 
+  volumes:
     - *docker-sock
     - *nginx-certs
     - ../../dhparam/ffdhe3072.pem:/etc/nginx/dhparam/dhparam.pem:ro
@@ -50,4 +50,4 @@ with_skip_backward:
   environment:
     - DHPARAM_GENERATION=false
   image: *img-nginxproxy
-  volumes: *vols-common
+  volumes: *vols-common