fix(document_loaders/telegram): fix pandas calls + add tests (#4806)

# Fix Telegram API loader + add tests.
I was testing this integration and it was broken with next error:
```python
message_threads = loader._get_message_threads(df)
KeyError: False
```
Also, this particular loader didn't have any tests / related group in
poetry, so I added those as well.

@hwchase17 / @eyurtsev please take a look on this fix PR.

---------

Co-authored-by: Dev 2049 <dev.dev2049@gmail.com>

tests/integration_tests/document_loaders/test_telegram.py

@@ -1,18 +0,0 @@
-from pathlib import Path
-
-from langchain.document_loaders import TelegramChatFileLoader
-
-
-def test_telegram_chat_file_loader() -> None:
-    """Test TelegramChatLoader."""
-    file_path = Path(__file__).parent.parent / "examples/telegram.json"
-    loader = TelegramChatFileLoader(str(file_path))
-    docs = loader.load()
-
-    assert len(docs) == 1
-    assert docs[0].metadata["source"] == str(file_path)
-    assert docs[0].page_content == (
-        "Henry on 2020-01-01T00:00:02: It's 2020...\n\n"
-        "Henry on 2020-01-01T00:00:04: Fireworks!\n\n"
-        "Grace 🧤 ðŸ\x8d’ on 2020-01-01T00:00:05: You're a minute late!\n\n"
-    )

tests/unit_tests/document_loaders/test_docs/telegram_channel.json

@@ -0,0 +1,34 @@
+[
+  {
+    "sender_id": -1111111,
+    "text": "Hello, world!",
+    "date": "2023-05-15T19:30:49+00:00",
+    "message.id": 1785,
+    "is_reply": false,
+    "reply_to_id": null
+  },
+  {
+    "sender_id": -1111111,
+    "text": "Telegram is the best!",
+    "date": "2023-05-08T20:17:10+00:00",
+    "message.id": 1784,
+    "is_reply": true,
+    "reply_to_id": 1783
+  },
+  {
+    "sender_id": -1111111,
+    "text": "Langchain is great.",
+    "date": "2023-05-03T23:43:33+00:00",
+    "message.id": 1783,
+    "is_reply": true,
+    "reply_to_id": 1782
+  },
+  {
+    "sender_id": -1111111,
+    "text": "LLMs are awesome!",
+    "date": "2023-05-03T15:32:25+00:00",
+    "message.id": 1782,
+    "is_reply": false,
+    "reply_to_id": null
+  }
+]

tests/unit_tests/document_loaders/test_telegram.py

@@ -0,0 +1,36 @@
+from pathlib import Path
+
+import pytest
+
+from langchain.document_loaders import TelegramChatApiLoader, TelegramChatFileLoader
+
+
+def test_telegram_chat_file_loader() -> None:
+    """Test TelegramChatFileLoader."""
+    file_path = Path(__file__).parent / "test_docs" / "telegram.json"
+    loader = TelegramChatFileLoader(str(file_path))
+    docs = loader.load()
+
+    assert len(docs) == 1
+    assert docs[0].metadata["source"] == str(file_path)
+    assert docs[0].page_content == (
+        "Henry on 2020-01-01T00:00:02: It's 2020...\n\n"
+        "Henry on 2020-01-01T00:00:04: Fireworks!\n\n"
+        "Grace 🧤 ðŸ\x8d’ on 2020-01-01T00:00:05: You're a minute late!\n\n"
+    )
+
+
+@pytest.mark.requires("telethon", "pandas")
+def test_telegram_channel_loader_parsing() -> None:
+    """Test TelegramChatApiLoader."""
+    file_path = Path(__file__).parent / "test_docs" / "telegram_channel.json"
+    # if we don't provide any value, it will skip fetching from telegram
+    # and will check the parsing logic.
+    loader = TelegramChatApiLoader(file_path=str(file_path))
+    docs = loader.load()
+
+    assert len(docs) == 1
+    print(docs[0].page_content)
+    assert docs[0].page_content == (
+        "Hello, world!.\nLLMs are awesome! Langchain is great. Telegram is the best!."
+    )