test(07-01): add failing tests for ZhihuLogin QR code login

TDD RED phase - tests expect ZhihuLogin class that doesn't exist yet:

- test_login_page_access: verify correct login URL
- test_qrcode_screenshot: verify QR code capture and save
- test_cookie_detection_with_z_c0: verify login detection
- test_cookie_detection_without_z_c0: verify no login when missing z_c0
- test_cookie_extraction: verify cookie string format
- test_login_timeout: verify timeout after 60s polling
- test_result_model_success: verify success result model
- test_result_model_failure: verify failure result model

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

tests/test_auth/test_qrcode_login.py

@@ -0,0 +1,147 @@
+"""Tests for ZhihuLogin QR code login functionality
+
+Tests the core login flow:
+1. Access login page
+2. Capture QR code screenshot
+3. Poll for login cookie (z_c0)
+4. Extract cookie string on success
+5. Handle timeout
+"""
+
+import pytest
+from unittest.mock import MagicMock, patch, AsyncMock
+from pathlib import Path
+
+
+class TestZhihuLogin:
+    """Test suite for ZhihuLogin class."""
+
+    def test_login_page_access(self, mock_browser):
+        """Test that login page is accessed with correct URL."""
+        from kb_workflow.auth import ZhihuLogin
+
+        login = ZhihuLogin(intermediate_path="/tmp/test")
+        login.browser = mock_browser
+
+        # Simulate calling goto
+        login.browser.goto("https://www.zhihu.com/signin")
+
+        # Verify goto was called with correct URL
+        mock_browser.goto.assert_called_once_with("https://www.zhihu.com/signin")
+
+    def test_qrcode_screenshot(self, mock_browser, mock_canvas, intermediate_path):
+        """Test QR code screenshot is captured and saved correctly."""
+        from kb_workflow.auth import ZhihuLogin
+
+        login = ZhihuLogin(intermediate_path=intermediate_path)
+        login.browser = mock_browser
+
+        # Mock the canvas screenshot
+        mock_browser.query_selector.return_value = mock_canvas
+        mock_canvas.screenshot.return_value = b"fake_png_bytes"
+
+        # Call _save_qrcode_image
+        screenshot_bytes = b"fake_png_bytes"
+        qrcode_path = login._save_qrcode_image(screenshot_bytes)
+
+        # Verify file was created
+        assert qrcode_path.exists()
+        assert qrcode_path.suffix == ".png"
+        assert "zhihu_qrcode" in qrcode_path.name
+
+    def test_cookie_detection_with_z_c0(self, mock_browser, sample_cookies):
+        """Test that login is detected when z_c0 cookie exists."""
+        from kb_workflow.auth import ZhihuLogin
+
+        login = ZhihuLogin(intermediate_path="/tmp/test")
+        login.browser = mock_browser
+
+        # Mock cookies to include z_c0
+        mock_browser.context.cookies.return_value = sample_cookies
+
+        # Check login cookie
+        is_logged_in = login.check_login_cookie()
+
+        assert is_logged_in is True
+
+    def test_cookie_detection_without_z_c0(self, mock_browser, sample_cookies_no_login):
+        """Test that login is NOT detected when z_c0 cookie is missing."""
+        from kb_workflow.auth import ZhihuLogin
+
+        login = ZhihuLogin(intermediate_path="/tmp/test")
+        login.browser = mock_browser
+
+        # Mock cookies without z_c0
+        mock_browser.context.cookies.return_value = sample_cookies_no_login
+
+        # Check login cookie
+        is_logged_in = login.check_login_cookie()
+
+        assert is_logged_in is False
+
+    def test_cookie_extraction(self, mock_browser, sample_cookies):
+        """Test cookie string extraction after successful login."""
+        from kb_workflow.auth import ZhihuLogin
+
+        login = ZhihuLogin(intermediate_path="/tmp/test")
+        login.browser = mock_browser
+
+        # Mock cookies
+        mock_browser.context.cookies.return_value = sample_cookies
+
+        # Get cookie string
+        cookie_str = login.get_cookies_str()
+
+        # Verify format: "name1=value1; name2=value2"
+        assert "z_c0=test_z_c0_value" in cookie_str
+        assert "_xsrf=test_xsrf_value" in cookie_str
+        assert ";" in cookie_str
+
+    def test_login_timeout(self, mock_browser, sample_cookies_no_login):
+        """Test that TimeoutError is raised after 60 seconds of polling."""
+        from kb_workflow.auth import ZhihuLogin
+        from tenacity import RetryError
+
+        login = ZhihuLogin(intermediate_path="/tmp/test", timeout=2)  # Short timeout for test
+        login.browser = mock_browser
+
+        # Mock cookies to always return no login
+        mock_browser.context.cookies.return_value = sample_cookies_no_login
+
+        # Should raise RetryError (wrapped by tenacity) or TimeoutError
+        with pytest.raises((TimeoutError, RetryError)):
+            login._wait_for_login()
+
+
+class TestZhihuLoginResult:
+    """Test suite for ZhihuLoginResult model."""
+
+    def test_result_model_success(self):
+        """Test ZhihuLoginResult model with successful login."""
+        from kb_workflow.auth import ZhihuLoginResult
+
+        result = ZhihuLoginResult(
+            success=True,
+            cookie_str="z_c0=abc123; _xsrf=xyz789",
+            qrcode_path=Path("/tmp/qrcode.png"),
+            error_message=None
+        )
+
+        assert result.success is True
+        assert "z_c0" in result.cookie_str
+        assert result.error_message is None
+
+    def test_result_model_failure(self):
+        """Test ZhihuLoginResult model with failed login."""
+        from kb_workflow.auth import ZhihuLoginResult
+
+        result = ZhihuLoginResult(
+            success=False,
+            cookie_str="",
+            qrcode_path=Path("/tmp/qrcode.png"),
+            error_message="Login timeout after 60 seconds"
+        )
+
+        assert result.success is False
+        assert result.cookie_str == ""
+        assert "timeout" in result.error_message.lower()