Added test

tests/test_http.py

@@ -0,0 +1,26 @@
+import pytest
+from discord import http
+
+
+class CustomResponse:
+    def __init__(self, text_data, content_type):
+        self._text = text_data
+        self.headers = {'content-type': content_type}
+
+    async def text(self, encoding='utf-8'):
+        return self._text
+
+
+@pytest.mark.asyncio
+async def test_json_or_text():
+    # Testing with json data
+    response = CustomResponse('{"key": "value"}', 'application/json')
+    result = await http.json_or_text(response)
+    assert isinstance(result, dict)
+    assert result == {"key": "value"}
+
+    # Testing with plain text data
+    response = CustomResponse('Hello world!', 'text/plain')
+    result = await http.json_or_text(response)
+    assert isinstance(result, str)
+    assert result == 'Hello world!'