fastapi-traffic/tests/test_exceptions.py

"""Tests for exceptions and error handling.

Comprehensive tests covering:
- Exception classes and their attributes
- Exception inheritance hierarchy
- Error message formatting
- Rate limit info in exceptions
- Configuration validation errors
"""

from __future__ import annotations

import pytest

from fastapi_traffic import BackendError, ConfigurationError, RateLimitExceeded
from fastapi_traffic.core.config import RateLimitConfig
from fastapi_traffic.core.models import RateLimitInfo
from fastapi_traffic.exceptions import FastAPITrafficError


class TestExceptionHierarchy:
    """Tests for exception class hierarchy."""

    def test_all_exceptions_inherit_from_base(self) -> None:
        """Test that all exceptions inherit from FastAPITrafficError."""
        assert issubclass(RateLimitExceeded, FastAPITrafficError)
        assert issubclass(BackendError, FastAPITrafficError)
        assert issubclass(ConfigurationError, FastAPITrafficError)

    def test_base_exception_inherits_from_exception(self) -> None:
        """Test that base exception inherits from Exception."""
        assert issubclass(FastAPITrafficError, Exception)

    def test_exceptions_are_catchable_as_base(self) -> None:
        """Test that all exceptions can be caught as base type."""
        try:
            raise RateLimitExceeded("test")
        except FastAPITrafficError:
            pass

        try:
            raise BackendError("test")
        except FastAPITrafficError:
            pass

        try:
            raise ConfigurationError("test")
        except FastAPITrafficError:
            pass


class TestRateLimitExceeded:
    """Tests for RateLimitExceeded exception."""

    def test_default_message(self) -> None:
        """Test default error message."""
        exc = RateLimitExceeded()
        assert exc.message == "Rate limit exceeded"
        assert str(exc) == "Rate limit exceeded"

    def test_custom_message(self) -> None:
        """Test custom error message."""
        exc = RateLimitExceeded("Custom rate limit message")
        assert exc.message == "Custom rate limit message"
        assert str(exc) == "Custom rate limit message"

    def test_retry_after_attribute(self) -> None:
        """Test retry_after attribute."""
        exc = RateLimitExceeded("test", retry_after=30.5)
        assert exc.retry_after == 30.5

    def test_retry_after_none_by_default(self) -> None:
        """Test retry_after is None by default."""
        exc = RateLimitExceeded("test")
        assert exc.retry_after is None

    def test_limit_info_attribute(self) -> None:
        """Test limit_info attribute."""
        info = RateLimitInfo(
            limit=100,
            remaining=0,
            reset_at=1234567890.0,
            retry_after=30.0,
        )
        exc = RateLimitExceeded("test", limit_info=info)
        assert exc.limit_info is not None
        assert exc.limit_info.limit == 100
        assert exc.limit_info.remaining == 0

    def test_limit_info_none_by_default(self) -> None:
        """Test limit_info is None by default."""
        exc = RateLimitExceeded("test")
        assert exc.limit_info is None

    def test_full_exception_construction(self) -> None:
        """Test constructing exception with all attributes."""
        info = RateLimitInfo(
            limit=50,
            remaining=0,
            reset_at=1234567890.0,
            retry_after=15.0,
            window_size=60.0,
        )
        exc = RateLimitExceeded(
            "API rate limit exceeded",
            retry_after=15.0,
            limit_info=info,
        )
        assert exc.message == "API rate limit exceeded"
        assert exc.retry_after == 15.0
        assert exc.limit_info is not None
        assert exc.limit_info.window_size == 60.0


class TestBackendError:
    """Tests for BackendError exception."""

    def test_default_message(self) -> None:
        """Test default error message."""
        exc = BackendError()
        assert exc.message == "Backend operation failed"

    def test_custom_message(self) -> None:
        """Test custom error message."""
        exc = BackendError("Redis connection failed")
        assert exc.message == "Redis connection failed"

    def test_original_error_attribute(self) -> None:
        """Test original_error attribute."""
        original = ValueError("Connection refused")
        exc = BackendError("Failed to connect", original_error=original)
        assert exc.original_error is original
        assert isinstance(exc.original_error, ValueError)

    def test_original_error_none_by_default(self) -> None:
        """Test original_error is None by default."""
        exc = BackendError("test")
        assert exc.original_error is None

    def test_chained_exception_handling(self) -> None:
        """Test that original error can be used for chaining."""
        original = ConnectionError("Network unreachable")
        exc = BackendError("Backend unavailable", original_error=original)

        assert exc.original_error is not None
        assert str(exc.original_error) == "Network unreachable"


class TestConfigurationError:
    """Tests for ConfigurationError exception."""

    def test_basic_construction(self) -> None:
        """Test basic exception construction."""
        exc = ConfigurationError("Invalid configuration")
        assert str(exc) == "Invalid configuration"

    def test_inherits_from_base(self) -> None:
        """Test inheritance from base exception."""
        exc = ConfigurationError("test")
        assert isinstance(exc, FastAPITrafficError)
        assert isinstance(exc, Exception)


class TestRateLimitConfigValidation:
    """Tests for RateLimitConfig validation errors."""

    def test_negative_limit_raises_error(self) -> None:
        """Test that negative limit raises ValueError."""
        with pytest.raises(ValueError, match="limit must be positive"):
            RateLimitConfig(limit=-1, window_size=60.0)

    def test_zero_limit_raises_error(self) -> None:
        """Test that zero limit raises ValueError."""
        with pytest.raises(ValueError, match="limit must be positive"):
            RateLimitConfig(limit=0, window_size=60.0)

    def test_negative_window_size_raises_error(self) -> None:
        """Test that negative window_size raises ValueError."""
        with pytest.raises(ValueError, match="window_size must be positive"):
            RateLimitConfig(limit=100, window_size=-1.0)

    def test_zero_window_size_raises_error(self) -> None:
        """Test that zero window_size raises ValueError."""
        with pytest.raises(ValueError, match="window_size must be positive"):
            RateLimitConfig(limit=100, window_size=0.0)

    def test_negative_cost_raises_error(self) -> None:
        """Test that negative cost raises ValueError."""
        with pytest.raises(ValueError, match="cost must be positive"):
            RateLimitConfig(limit=100, window_size=60.0, cost=-1)

    def test_zero_cost_raises_error(self) -> None:
        """Test that zero cost raises ValueError."""
        with pytest.raises(ValueError, match="cost must be positive"):
            RateLimitConfig(limit=100, window_size=60.0, cost=0)

    def test_valid_config_does_not_raise(self) -> None:
        """Test that valid configuration does not raise."""
        config = RateLimitConfig(limit=100, window_size=60.0, cost=1)
        assert config.limit == 100
        assert config.window_size == 60.0
        assert config.cost == 1


class TestRateLimitInfo:
    """Tests for RateLimitInfo model."""

    def test_to_headers_basic(self) -> None:
        """Test basic header generation."""
        info = RateLimitInfo(
            limit=100,
            remaining=50,
            reset_at=1234567890.0,
        )
        headers = info.to_headers()
        assert headers["X-RateLimit-Limit"] == "100"
        assert headers["X-RateLimit-Remaining"] == "50"
        assert headers["X-RateLimit-Reset"] == "1234567890"

    def test_to_headers_with_retry_after(self) -> None:
        """Test header generation with retry_after."""
        info = RateLimitInfo(
            limit=100,
            remaining=0,
            reset_at=1234567890.0,
            retry_after=30.0,
        )
        headers = info.to_headers()
        assert "Retry-After" in headers
        assert headers["Retry-After"] == "30"

    def test_to_headers_without_retry_after(self) -> None:
        """Test header generation without retry_after."""
        info = RateLimitInfo(
            limit=100,
            remaining=50,
            reset_at=1234567890.0,
        )
        headers = info.to_headers()
        assert "Retry-After" not in headers

    def test_remaining_cannot_be_negative_in_headers(self) -> None:
        """Test that remaining is clamped to 0 in headers."""
        info = RateLimitInfo(
            limit=100,
            remaining=-5,
            reset_at=1234567890.0,
        )
        headers = info.to_headers()
        assert headers["X-RateLimit-Remaining"] == "0"

    def test_frozen_dataclass(self) -> None:
        """Test that RateLimitInfo is immutable."""
        info = RateLimitInfo(
            limit=100,
            remaining=50,
            reset_at=1234567890.0,
        )
        with pytest.raises(AttributeError):
            info.limit = 200  # type: ignore[misc]

    def test_default_window_size(self) -> None:
        """Test default window_size value."""
        info = RateLimitInfo(
            limit=100,
            remaining=50,
            reset_at=1234567890.0,
        )
        assert info.window_size == 60.0