test(03-02): add failing tests for printer detail page

- test_printer_detail_shows_driver: asserts driver name appears on detail page
- test_printer_detail_not_found: asserts 404 for missing printer ID
- test_printer_detail_no_driver: asserts graceful display when driver is None

tests/test_printer_crud.py

@@ -1,4 +1,6 @@
 """Integration tests for printer and client CRUD endpoints."""
+import json
+
 import pytest
 from fastapi.testclient import TestClient
 
@@ -181,6 +183,54 @@ def test_create_printer_invalid_ip(client: TestClient) -> None:
     assert resp.status_code == 400
 
 
+def test_printer_detail_shows_driver(client: TestClient) -> None:
+    """GET /printers/{id} returns 200 with all printer fields and driver name."""
+    from imptune.db.models import Driver, Printer
+
+    driver_obj = Driver.create(
+        sha256="abc123",
+        original_filename="hp_universal.zip",
+        size_bytes=1000,
+        driver_desc=json.dumps(["HP Universal"]),
+    )
+    printer = Printer.create(
+        name="HP Office Printer",
+        ip_address="10.0.1.1",
+        port_name="IP_10_0_1_1",
+        driver=driver_obj,
+    )
+
+    resp = client.get(f"/printers/{printer.id}")
+    assert resp.status_code == 200
+    html = resp.text
+    assert "HP Office Printer" in html
+    assert "10.0.1.1" in html
+    assert "HP Universal" in html
+
+
+def test_printer_detail_not_found(client: TestClient) -> None:
+    """GET /printers/9999 returns 404."""
+    resp = client.get("/printers/9999")
+    assert resp.status_code == 404
+
+
+def test_printer_detail_no_driver(client: TestClient) -> None:
+    """GET /printers/{id} for printer with no driver returns 200 with 'No driver assigned'."""
+    from imptune.db.models import Printer
+
+    printer = Printer.create(
+        name="Driverless Printer",
+        ip_address="10.0.1.2",
+        port_name="IP_10_0_1_2",
+        driver=None,
+    )
+
+    resp = client.get(f"/printers/{printer.id}")
+    assert resp.status_code == 200
+    html = resp.text
+    assert "No driver assigned" in html
+
+
 def test_delete_printer(client: TestClient) -> None:
     """DELETE /printers/{id} removes the printer; GET /printers no longer shows it."""
     from imptune.db.models import Printer