test(10-02): add health check tests for proxy pool

- test_fail_threshold: verify 3 consecutive failures mark proxy unavailable
- test_success_resets_count: verify success resets failure count
- test_cooldown_recovery: verify proxy recovers after cooldown
- test_cooldown_not_elapsed: verify proxy stays unavailable during cooldown
- test_all_unavailable_fallback: verify fallback to first proxy when all fail
- test_get_available_count: verify available proxy count tracking

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_crawler/test_proxy_pool.py

@@ -176,3 +176,131 @@ class TestProxyEntry:
         assert entry.fail_count == 0
         assert entry.last_fail_time is None
         assert entry.is_available is True
+
+    def test_fail_threshold(self):
+        """Test that proxy becomes unavailable after 3 consecutive failures."""
+        entry = ProxyEntry(url="http://proxy:8080")
+
+        # First two failures should not mark as unavailable
+        entry.record_failure(max_fail_count=3)
+        assert entry.fail_count == 1
+        assert entry.is_available is True
+
+        entry.record_failure(max_fail_count=3)
+        assert entry.fail_count == 2
+        assert entry.is_available is True
+
+        # Third failure should mark as unavailable
+        entry.record_failure(max_fail_count=3)
+        assert entry.fail_count == 3
+        assert entry.is_available is False
+
+    def test_success_resets_count(self):
+        """Test that recording success resets failure count and restores availability."""
+        entry = ProxyEntry(url="http://proxy:8080")
+
+        # Record some failures
+        entry.record_failure(max_fail_count=3)
+        entry.record_failure(max_fail_count=3)
+        assert entry.fail_count == 2
+
+        # Record success
+        entry.record_success()
+
+        assert entry.fail_count == 0
+        assert entry.is_available is True
+
+    def test_cooldown_recovery(self):
+        """Test that failed proxy recovers after cooldown period."""
+        import time
+
+        entry = ProxyEntry(url="http://proxy:8080")
+
+        # Mark as unavailable
+        entry.record_failure(max_fail_count=3)
+        entry.record_failure(max_fail_count=3)
+        entry.record_failure(max_fail_count=3)
+        assert entry.is_available is False
+
+        # Wait for cooldown (using short cooldown for testing)
+        time.sleep(1)
+
+        # Check recovery with 1 second cooldown
+        result = entry.check_recovery(cooldown_seconds=1)
+        assert result is True
+        assert entry.is_available is True
+        assert entry.fail_count == 0
+
+    def test_cooldown_not_elapsed(self):
+        """Test that failed proxy does not recover before cooldown period."""
+        entry = ProxyEntry(url="http://proxy:8080")
+
+        # Mark as unavailable
+        entry.record_failure(max_fail_count=3)
+        entry.record_failure(max_fail_count=3)
+        entry.record_failure(max_fail_count=3)
+        assert entry.is_available is False
+
+        # Check recovery immediately with 60 second cooldown
+        result = entry.check_recovery(cooldown_seconds=60)
+        assert result is False
+        assert entry.is_available is False
+
+
+class TestProxyPoolHealthCheck:
+    """Tests for ProxyPool health check and availability methods."""
+
+    def test_all_unavailable_fallback(self):
+        """Test that get_next_proxy returns first proxy when all are unavailable."""
+        config = ProxyPoolConfig(
+            proxies=[
+                "http://proxy-a:8080",
+                "http://proxy-b:8080",
+                "http://proxy-c:8080",
+            ],
+            max_fail_count=3
+        )
+        pool = ProxyPool(config)
+
+        # Mark all proxies as unavailable
+        for _ in range(3):
+            pool._entries[0].record_failure(max_fail_count=3)
+            pool._entries[1].record_failure(max_fail_count=3)
+            pool._entries[2].record_failure(max_fail_count=3)
+
+        # All should be unavailable
+        assert pool._entries[0].is_available is False
+        assert pool._entries[1].is_available is False
+        assert pool._entries[2].is_available is False
+
+        # Should fallback to first proxy
+        proxy = pool.get_next_proxy()
+        assert proxy is not None
+        assert proxy.url == "http://proxy-a:8080"
+
+    def test_get_available_count(self):
+        """Test that get_available_count returns correct number of available proxies."""
+        config = ProxyPoolConfig(
+            proxies=[
+                "http://proxy-a:8080",
+                "http://proxy-b:8080",
+                "http://proxy-c:8080",
+            ],
+            max_fail_count=3
+        )
+        pool = ProxyPool(config)
+
+        # Initially all available
+        assert pool.get_available_count() == 3
+
+        # Mark one as unavailable
+        for _ in range(3):
+            pool._entries[0].record_failure(max_fail_count=3)
+
+        assert pool.get_available_count() == 2
+
+        # Mark another as unavailable
+        for _ in range(3):
+            pool._entries[1].record_failure(max_fail_count=3)
+
+        assert pool.get_available_count() == 1