Fix failing cost calculation test

When updating the model pricing in commit 50fa0cc5ae I forgot to update
the associated test. As well as fixing this test, this commit also
updates the calculation to use `math.floor` instead of `round` to round
to six decimal places. This is because the `round` function appeared to
round incorrectly. For example, when running the test, 0.0000275 was
rounded to 0.000028 instead of the expected 0.000028.

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "llm-chat"
-version = "1.1.2"
+version = "1.1.3"
 description = "A general CLI interface for large language models."
 authors = ["Paul Harrison <paul@harrison.sh>"]
 readme = "README.md"

src/llm_chat/chat.py

@@ -1,3 +1,4 @@
+import math
 from datetime import datetime
 from enum import StrEnum, auto
 from pathlib import Path
@@ -177,13 +178,14 @@ class Chat:
         """Calculate the cost of a request."""
         self.conversation.completion_tokens += usage.completion_tokens
         self.conversation.prompt_tokens += usage.prompt_tokens
-        self.conversation.cost = round(
+        self.conversation.cost = math.floor(
+            1000000 * (
                 (self.conversation.completion_tokens / 1000)
                 * self._pricing[self.settings.model][Token.COMPLETION]
                 + (self.conversation.prompt_tokens / 1000)
-            * self._pricing[self.settings.model][Token.PROMPT],
-            6,
+                * self._pricing[self.settings.model][Token.PROMPT]
             )
+        ) / 1000000
 
     def save(self) -> None:
         """Save the conversation to the history directory."""

tests/test_chat.py

@@ -116,7 +116,7 @@ def test_send_message() -> None:
         assert response == "Hello!"
 
 
-@pytest.mark.parametrize("model,cost", [(Model.GPT3, 0.000043), (Model.GPT4, 0.00105)])
+@pytest.mark.parametrize("model,cost", [(Model.GPT3, round(0.000027, 6)), (Model.GPT4, 0.00105)])
 def test_calculate_cost(model: Model, cost: float) -> None:
     with patch("llm_chat.chat.Chat._make_request") as mock_make_request:
         mock_make_request.return_value = ChatCompletion(