tests: improve Shamir persistence test

tests/upgrade_tests/test_shamir_persistence.py

@@ -14,6 +14,8 @@
 # You should have received a copy of the License along with this library.
 # If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.
 
+import pytest
+
 from trezorlib import device
 
 from .. import buttons
@@ -29,11 +31,16 @@ def enter_word(debug, word):
     return debug.click(buttons.CONFIRM_WORD, wait=True)
 
 
+@pytest.fixture
+def emulator():
+    emu = EmulatorWrapper("core")
+    with emu:
+        yield emu
+
+
 @core_only
-def test_persistence():
-    with EmulatorWrapper("core") as emu, BackgroundDeviceHandler(
-        emu.client
-    ) as device_handler:
+def test_persistence(emulator):
+    device_handler = BackgroundDeviceHandler(emulator.client)
     debug = device_handler.debuglink()
     features = device_handler.features()
 
@@ -46,12 +53,7 @@ def test_persistence():
     layout = debug.click(buttons.OK, wait=True)
     assert "Select number of words" in layout.text
 
-        storage = emu.storage()
-        device_handler.kill_task()
-
-    with EmulatorWrapper("core", storage=storage) as emu, BackgroundDeviceHandler(
-        emu.client
-    ) as device_handler:
+    device_handler.restart(emulator)
     debug = device_handler.debuglink()
     features = device_handler.features()