bugfix: tests: Fix tests failing on WSL systems.

Addressed issues with file path separators `\\` and GUI return codes
specific to WSL environments.

Author: rsashank

tests/helper/test_helper.py

@@ -21,6 +21,7 @@
     process_media,
     sort_unread_topics,
 )
+from zulipterminal.platform_code import PLATFORM
 
 
 MODULE = "zulipterminal.helper"
@@ -539,6 +540,9 @@ def test_download_media(
     ) = media_path
     controller = mocker.Mock()
 
+    if PLATFORM == "WSL":
+        media_path = media_path.replace("/", "\\")
+
     assert media_path == download_media(controller, url, callback)
 
 
@@ -604,14 +608,14 @@ def test_process_media_empty_url(
 @pytest.mark.parametrize(
     "returncode, error",
     [
-        (0, []),
+        (1 if PLATFORM == "WSL" else 0, []),
         (
-            1,
+            0 if PLATFORM == "WSL" else 1,
             [
                 " The tool ",
                 ("footer_contrast", "xdg-open"),
                 " did not run successfully" ". Exited with ",
-                ("footer_contrast", "1"),
+                ("footer_contrast", "0" if PLATFORM == "WSL" else "1"),
             ],
         ),
     ],