feat(test): Phase 1.5 coverage expansion - COV-001 to COV-013

Coverage baseline raised from 13.65% to 26% (+12.35%)
Gate raised from 12% to 18%

Tasks completed:
- COV-001: Command system unit tests (100% coverage)
- COV-002: API service unit tests batch 1 (user/apikey/model/provider)
- COV-003: Provider model manager unit tests
- COV-004: Pipeline remaining stage tests (aggregator/cntfilter/longtext/msgtrun)
- COV-005: Storage and utils coverage pass
- COV-006: Gate ratchet 12%→15%
- COV-007: Gate ratchet 15%→18%
- COV-008: API service batch 2 (bot/pipeline/webhook/space/maintenance/mcp)
- COV-009: Blocked - API controller circular import issue documented
- COV-010: Plugin runtime unit tests (+0.08%)
- COV-011: RAG and vector unit tests (+0.68%)
- COV-012: Core boot and migration unit tests
- COV-013: Provider requester logic unit tests (+0.62%)

Key additions:
- tests/utils/import_isolation.py: sys.modules isolation for circular imports
- Provider requester mock tests: proved HTTP-dependent code can be tested locally
- Vector filter utilities: 100% coverage on pure functions
- API services: fake persistence pattern for unit testing

Blocked issue COV-009 documented in langbot-test-plan/1.5/issues/

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/unit_tests/provider/runners/test_difysvapi_runner.py

@@ -0,0 +1,169 @@
+"""Tests for DifyServiceAPIRunner pure utility methods.
+
+Tests the helper methods that don't require real Dify API calls.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+
+class TestDifyExtractTextOutput:
+    """Tests for _extract_dify_text_output method."""
+
+    def _create_runner(self):
+        """Create runner instance."""
+        from unittest.mock import MagicMock
+
+        from langbot.pkg.provider.runners.difysvapi import DifyServiceAPIRunner
+
+        mock_app = MagicMock()
+        pipeline_config = {
+            'ai': {
+                'dify-service-api': {
+                    'app-type': 'chat',
+                    'api-key': 'test-key',
+                    'base-url': 'https://api.dify.ai',
+                }
+            },
+            'output': {'misc': {}}
+        }
+
+        runner = DifyServiceAPIRunner(mock_app, pipeline_config)
+        runner.dify_client = MagicMock()
+
+        return runner
+
+    def test_extract_none_value(self):
+        """None returns empty string."""
+        runner = self._create_runner()
+
+        result = runner._extract_dify_text_output(None)
+
+        assert result == ''
+
+    def test_extract_string_value(self):
+        """Plain string is returned."""
+        runner = self._create_runner()
+
+        result = runner._extract_dify_text_output('plain text')
+
+        assert result == 'plain text'
+
+    def test_extract_dict_with_content(self):
+        """Dict with 'content' key extracts content."""
+        runner = self._create_runner()
+
+        result = runner._extract_dify_text_output({'content': 'extracted content'})
+
+        assert result == 'extracted content'
+
+    def test_extract_dict_without_content(self):
+        """Dict without 'content' key is JSON dumped."""
+        runner = self._create_runner()
+
+        result = runner._extract_dify_text_output({'key': 'value'})
+
+        assert 'key' in result
+        assert 'value' in result
+
+    def test_extract_json_string_with_content(self):
+        """JSON string with 'content' key extracts content."""
+        runner = self._create_runner()
+
+        result = runner._extract_dify_text_output('{"content": "json content"}')
+
+        assert result == 'json content'
+
+    def test_extract_json_string_without_content(self):
+        """JSON string without 'content' key returns original."""
+        runner = self._create_runner()
+
+        result = runner._extract_dify_text_output('{"other": "value"}')
+
+        assert '{"other": "value"}' in result
+
+    def test_extract_whitespace_string(self):
+        """Whitespace string returns empty."""
+        runner = self._create_runner()
+
+        result = runner._extract_dify_text_output('   ')
+
+        assert result == ''
+
+
+class TestDifyRunnerConfigValidation:
+    """Tests for runner config validation."""
+
+    def test_invalid_app_type_raises(self):
+        """Invalid app-type raises DifyAPIError."""
+        from unittest.mock import MagicMock
+
+        from langbot.pkg.provider.runners.difysvapi import DifyServiceAPIRunner
+        from langbot.libs.dify_service_api.v1.errors import DifyAPIError
+
+        mock_app = MagicMock()
+        pipeline_config = {
+            'ai': {
+                'dify-service-api': {
+                    'app-type': 'invalid-type',
+                    'api-key': 'test',
+                    'base-url': 'https://api.dify.ai',
+                }
+            },
+            'output': {'misc': {}}
+        }
+
+        with pytest.raises(DifyAPIError, match='不支持'):
+            DifyServiceAPIRunner(mock_app, pipeline_config)
+
+    def test_valid_app_types(self):
+        """Valid app-types don't raise."""
+        from unittest.mock import MagicMock
+
+        from langbot.pkg.provider.runners.difysvapi import DifyServiceAPIRunner
+
+        mock_app = MagicMock()
+
+        for app_type in ['chat', 'agent', 'workflow']:
+            pipeline_config = {
+                'ai': {
+                    'dify-service-api': {
+                        'app-type': app_type,
+                        'api-key': 'test',
+                        'base-url': 'https://api.dify.ai',
+                    }
+                },
+                'output': {'misc': {}}
+            }
+
+            runner = DifyServiceAPIRunner(mock_app, pipeline_config)
+            # Should not raise
+            assert runner is not None
+
+
+class TestDifyRunnerInit:
+    """Tests for runner initialization."""
+
+    def test_runner_stores_config(self):
+        """Runner stores pipeline_config."""
+        from unittest.mock import MagicMock
+
+        from langbot.pkg.provider.runners.difysvapi import DifyServiceAPIRunner
+
+        mock_app = MagicMock()
+        pipeline_config = {
+            'ai': {
+                'dify-service-api': {
+                    'app-type': 'chat',
+                    'api-key': 'test-key',
+                    'base-url': 'https://api.dify.ai',
+                }
+            },
+            'output': {'misc': {}}
+        }
+
+        runner = DifyServiceAPIRunner(mock_app, pipeline_config)
+
+        assert runner.pipeline_config == pipeline_config
+        assert runner.ap == mock_app