fix(parallel_request_limiter.py): handle tpm/rpm limits being null

tests/README.MD

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+Most tests are in `/litellm/tests`. These are just the tests for the proxy docker image, used for circle ci. 

tests/test_chat_completion.py

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+# What this tests ?
+## Tests /chat/completions by generating a key and then making a chat completions request
+import pytest
+import asyncio
+import aiohttp
+
+
+async def generate_key(session):
+    url = "http://0.0.0.0:4000/key/generate"
+    headers = {"Authorization": "Bearer sk-1234", "Content-Type": "application/json"}
+    data = {
+        "models": ["gpt-4"],
+        "duration": None,
+    }
+
+    async with session.post(url, headers=headers, json=data) as response:
+        status = response.status
+        response_text = await response.text()
+
+        print(response_text)
+        print()
+
+        if status != 200:
+            raise Exception(f"Request did not return a 200 status code: {status}")
+        return await response.json()
+
+
+async def chat_completion(session, key):
+    url = "http://0.0.0.0:4000/chat/completions"
+    headers = {
+        "Authorization": f"Bearer {key}",
+        "Content-Type": "application/json",
+    }
+    data = {
+        "model": "gpt-4",
+        "messages": [
+            {"role": "system", "content": "You are a helpful assistant."},
+            {"role": "user", "content": "Hello!"},
+        ],
+    }
+
+    async with session.post(url, headers=headers, json=data) as response:
+        status = response.status
+        response_text = await response.text()
+
+        print(response_text)
+        print()
+
+        if status != 200:
+            raise Exception(f"Request did not return a 200 status code: {status}")
+
+
+@pytest.mark.asyncio
+async def test_key_gen():
+    async with aiohttp.ClientSession() as session:
+        key_gen = await generate_key(session=session)
+        key = key_gen["key"]
+        await chat_completion(session=session, key=key)

tests/test_parallel_key_gen.py

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+# What this tests ?
+## Tests /key/generate by making 10 parallel requests, and asserting all are successful
+import pytest
+import asyncio
+import aiohttp
+
+
+async def generate_key(session, i):
+    url = "http://0.0.0.0:4000/key/generate"
+    headers = {"Authorization": "Bearer sk-1234", "Content-Type": "application/json"}
+    data = {
+        "models": ["azure-models"],
+        "aliases": {"mistral-7b": "gpt-3.5-turbo"},
+        "duration": None,
+    }
+
+    async with session.post(url, headers=headers, json=data) as response:
+        status = response.status
+        response_text = await response.text()
+
+        print(f"Response {i} (Status code: {status}):")
+        print(response_text)
+        print()
+
+        if status != 200:
+            raise Exception(f"Request {i} did not return a 200 status code: {status}")
+
+
+@pytest.mark.asyncio
+async def test_key_gen():
+    async with aiohttp.ClientSession() as session:
+        tasks = [generate_key(session, i) for i in range(1, 11)]
+        await asyncio.gather(*tasks)