Add tests for OAuth client and webhook notification handling

- Implement tests for `EbayOAuthClient` to verify authorization URL generation with configured scopes and token reuse logic.
- Add tests for `WebhookChallengeHandler` to ensure correct SHA256 response generation and for `WebhookSignatureParser` to validate extraction of known fields from signature strings.

scripts/generate_clients.py

@@ -0,0 +1,134 @@
+from __future__ import annotations
+
+import argparse
+import shutil
+import subprocess
+import sys
+import tempfile
+from dataclasses import dataclass
+from pathlib import Path
+
+import yaml
+
+
+ROOT = Path(__file__).resolve().parent.parent
+GENERATED_ROOT = ROOT / "ebay_client" / "generated"
+
+
+@dataclass(frozen=True)
+class ApiSpec:
+    name: str
+    spec_path: Path
+    output_path: Path
+    project_name: str
+    package_name: str
+
+
+API_SPECS = {
+    "notification": ApiSpec(
+        name="notification",
+        spec_path=ROOT / "commerce_notification_v1_oas3.yaml",
+        output_path=GENERATED_ROOT / "notification",
+        project_name="ebay-notification-generated",
+        package_name="notification_generated",
+    ),
+    "inventory": ApiSpec(
+        name="inventory",
+        spec_path=ROOT / "sell_inventory_v1_oas3.yaml",
+        output_path=GENERATED_ROOT / "inventory",
+        project_name="ebay-inventory-generated",
+        package_name="inventory_generated",
+    ),
+    "fulfillment": ApiSpec(
+        name="fulfillment",
+        spec_path=ROOT / "sell_fulfillment_v1_oas3.yaml",
+        output_path=GENERATED_ROOT / "fulfillment",
+        project_name="ebay-fulfillment-generated",
+        package_name="fulfillment_generated",
+    ),
+    "account": ApiSpec(
+        name="account",
+        spec_path=ROOT / "sell_account_v1_oas3.yaml",
+        output_path=GENERATED_ROOT / "account",
+        project_name="ebay-account-generated",
+        package_name="account_generated",
+    ),
+    "feed": ApiSpec(
+        name="feed",
+        spec_path=ROOT / "sell_feed_v1_oas3.yaml",
+        output_path=GENERATED_ROOT / "feed",
+        project_name="ebay-feed-generated",
+        package_name="feed_generated",
+    ),
+}
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser(description="Generate isolated low-level clients from the eBay OpenAPI contracts.")
+    parser.add_argument("--api", choices=sorted(API_SPECS), help="Generate only one API package.")
+    parser.add_argument("--fail-on-warning", action="store_true", help="Fail if the generator emits warnings.")
+    return parser.parse_args()
+
+
+def build_config(spec: ApiSpec) -> dict[str, object]:
+    return {
+        "project_name_override": spec.project_name,
+        "package_name_override": spec.package_name,
+        "field_prefix": "field_",
+        "generate_all_tags": False,
+        "http_timeout": 30,
+        "literal_enums": False,
+        "post_hooks": [],
+        "use_path_prefixes_for_title_model_names": False,
+    }
+
+
+def run_generation(spec: ApiSpec, *, fail_on_warning: bool) -> None:
+        if not spec.spec_path.exists():
+            raise FileNotFoundError(f"OpenAPI spec not found: {spec.spec_path}")
+
+        with tempfile.TemporaryDirectory(prefix=f"ebay_{spec.name}_") as temp_dir_name:
+            temp_dir = Path(temp_dir_name)
+            config_path = temp_dir / "config.yaml"
+            temp_output = temp_dir / "output"
+            config_path.write_text(yaml.safe_dump(build_config(spec), sort_keys=True), encoding="utf-8")
+
+            command = [
+                sys.executable,
+                "-m",
+                "openapi_python_client",
+                "generate",
+                "--path",
+                str(spec.spec_path),
+                "--meta",
+                "none",
+                "--overwrite",
+                "--config",
+                str(config_path),
+                "--output-path",
+                str(temp_output),
+            ]
+            if fail_on_warning:
+                command.append("--fail-on-warning")
+
+            subprocess.run(command, check=True, cwd=str(ROOT))
+
+            generated_package = temp_output / spec.package_name
+            if not generated_package.exists():
+                generated_package = temp_output
+            if spec.output_path.exists():
+                shutil.rmtree(spec.output_path)
+            shutil.copytree(generated_package, spec.output_path)
+
+
+def main() -> int:
+    args = parse_args()
+    specs = [API_SPECS[args.api]] if args.api else [API_SPECS[name] for name in sorted(API_SPECS)]
+    for spec in specs:
+        print(f"Generating {spec.name} from {spec.spec_path.name} -> {spec.output_path}")
+        run_generation(spec, fail_on_warning=args.fail_on_warning)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())