Refactor tethering utility methods

This is no-op refactoring to extract tethering utility methods
to a standalone file, and split setup and clean up process
to allow new test cases can perform custom verifications.

Also, this CL makes connectToWifi returns NetworkHandle for later use.

Test: m connectivity_multi_devices_snippet && \
      atest CtsConnectivityMultiDevicesTestCases:ConnectivityMultiDevicesTest
Bug: 335368434
Change-Id: Ib0df28107fd09b573db1e51ff624d0f027bda23d
diff --git a/tests/cts/multidevices/Android.bp b/tests/cts/multidevices/Android.bp
index 5ac4229..b819788 100644
--- a/tests/cts/multidevices/Android.bp
+++ b/tests/cts/multidevices/Android.bp
@@ -19,7 +19,10 @@
 python_test_host {
     name: "CtsConnectivityMultiDevicesTestCases",
     main: "connectivity_multi_devices_test.py",
-    srcs: ["connectivity_multi_devices_test.py"],
+    srcs: [
+        "connectivity_multi_devices_test.py",
+        "tether_utils.py",
+    ],
     libs: [
         "mobly",
     ],
diff --git a/tests/cts/multidevices/connectivity_multi_devices_test.py b/tests/cts/multidevices/connectivity_multi_devices_test.py
index ab88504..417db99 100644
--- a/tests/cts/multidevices/connectivity_multi_devices_test.py
+++ b/tests/cts/multidevices/connectivity_multi_devices_test.py
@@ -1,23 +1,16 @@
 # Lint as: python3
 """Connectivity multi devices tests."""
-import base64
 import sys
-import uuid
-
-from mobly import asserts
 from mobly import base_test
 from mobly import test_runner
 from mobly import utils
 from mobly.controllers import android_device
+import tether_utils
+from tether_utils import UpstreamType
 
 CONNECTIVITY_MULTI_DEVICES_SNIPPET_PACKAGE = "com.google.snippet.connectivity"
 
 
-class UpstreamType:
-  CELLULAR = 1
-  WIFI = 2
-
-
 class ConnectivityMultiDevicesTest(base_test.BaseTestClass):
 
   def setup_class(self):
@@ -40,66 +33,27 @@
         raise_on_exception=True,
     )
 
-  @staticmethod
-  def generate_uuid32_base64():
-    """Generates a UUID32 and encodes it in Base64.
-
-    Returns:
-        str: The Base64-encoded UUID32 string. Which is 22 characters.
-    """
-    return base64.b64encode(uuid.uuid1().bytes).decode("utf-8").strip("=")
-
-  def _do_test_hotspot_for_upstream_type(self, upstream_type):
-    """Test hotspot with the specified upstream type.
-
-    This test create a hotspot, make the client connect
-    to it, and verify the packet is forwarded by the hotspot.
-    """
-    server = self.serverDevice.connectivity_multi_devices_snippet
-    client = self.clientDevice.connectivity_multi_devices_snippet
-
-    # Assert pre-conditions specific to each upstream type.
-    asserts.skip_if(not client.hasWifiFeature(), "Client requires Wifi feature")
-    asserts.skip_if(
-      not server.hasHotspotFeature(), "Server requires hotspot feature"
-    )
-    if upstream_type == UpstreamType.CELLULAR:
-      asserts.skip_if(
-          not server.hasTelephonyFeature(), "Server requires Telephony feature"
-      )
-      server.requestCellularAndEnsureDefault()
-    elif upstream_type == UpstreamType.WIFI:
-      asserts.skip_if(
-          not server.isStaApConcurrencySupported(),
-          "Server requires Wifi AP + STA concurrency",
-      )
-      server.ensureWifiIsDefault()
-    else:
-      raise ValueError(f"Invalid upstream type: {upstream_type}")
-
-    # Generate ssid/passphrase with random characters to make sure nearby devices won't
-    # connect unexpectedly. Note that total length of ssid cannot go over 32.
-    testSsid = "HOTSPOT-" + self.generate_uuid32_base64()
-    testPassphrase = self.generate_uuid32_base64()
-
-    try:
-      # Create a hotspot with fixed SSID and password.
-      server.startHotspot(testSsid, testPassphrase)
-
-      # Make the client connects to the hotspot.
-      client.connectToWifi(testSsid, testPassphrase, True)
-
-    finally:
-      if upstream_type == UpstreamType.CELLULAR:
-        server.unrequestCellular()
-      # Teardown the hotspot.
-      server.stopAllTethering()
-
   def test_hotspot_upstream_wifi(self):
-    self._do_test_hotspot_for_upstream_type(UpstreamType.WIFI)
+    try:
+      # Connectivity of the client verified by asserting the validated capability.
+      tether_utils.setup_hotspot_and_client_for_upstream_type(
+          self.serverDevice, self.clientDevice, UpstreamType.WIFI
+      )
+    finally:
+      tether_utils.cleanup_tethering_for_upstream_type(
+          self.serverDevice, UpstreamType.WIFI
+      )
 
   def test_hotspot_upstream_cellular(self):
-    self._do_test_hotspot_for_upstream_type(UpstreamType.CELLULAR)
+    try:
+      # Connectivity of the client verified by asserting the validated capability.
+      tether_utils.setup_hotspot_and_client_for_upstream_type(
+          self.serverDevice, self.clientDevice, UpstreamType.CELLULAR
+      )
+    finally:
+      tether_utils.cleanup_tethering_for_upstream_type(
+          self.serverDevice, UpstreamType.CELLULAR
+      )
 
 
 if __name__ == "__main__":
diff --git a/tests/cts/multidevices/snippet/ConnectivityMultiDevicesSnippet.kt b/tests/cts/multidevices/snippet/ConnectivityMultiDevicesSnippet.kt
index 543dc03..8805edd 100644
--- a/tests/cts/multidevices/snippet/ConnectivityMultiDevicesSnippet.kt
+++ b/tests/cts/multidevices/snippet/ConnectivityMultiDevicesSnippet.kt
@@ -21,7 +21,6 @@
 import android.content.pm.PackageManager.FEATURE_TELEPHONY
 import android.content.pm.PackageManager.FEATURE_WIFI
 import android.net.ConnectivityManager
-import android.net.Network
 import android.net.NetworkCapabilities.NET_CAPABILITY_VALIDATED
 import android.net.NetworkCapabilities.TRANSPORT_WIFI
 import android.net.NetworkRequest
@@ -93,7 +92,7 @@
     // Suppress warning because WifiManager methods to connect to a config are
     // documented not to be deprecated for privileged users.
     @Suppress("DEPRECATION")
-    fun connectToWifi(ssid: String, passphrase: String, requireValidation: Boolean): Network {
+    fun connectToWifi(ssid: String, passphrase: String): Long {
         val specifier = WifiNetworkSpecifier.Builder()
             .setBand(ScanResult.WIFI_BAND_24_GHZ)
             .build()
@@ -126,7 +125,7 @@
                 // Remove double quotes.
                 val ssidFromCaps = (WifiInfo::sanitizeSsid)(it.caps.ssid)
                 ssidFromCaps == ssid && it.caps.hasCapability(NET_CAPABILITY_VALIDATED)
-            }.network
+            }.network.networkHandle
         }
     }
 
diff --git a/tests/cts/multidevices/tether_utils.py b/tests/cts/multidevices/tether_utils.py
new file mode 100644
index 0000000..a2d703c
--- /dev/null
+++ b/tests/cts/multidevices/tether_utils.py
@@ -0,0 +1,103 @@
+#  Copyright (C) 2024 The Android Open Source Project
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+import base64
+import uuid
+
+from mobly import asserts
+from mobly.controllers import android_device
+
+
+class UpstreamType:
+  CELLULAR = 1
+  WIFI = 2
+
+
+def generate_uuid32_base64() -> str:
+  """Generates a UUID32 and encodes it in Base64.
+
+  Returns:
+      str: The Base64-encoded UUID32 string. Which is 22 characters.
+  """
+  # Strip padding characters to make it safer for hotspot name length limit.
+  return base64.b64encode(uuid.uuid1().bytes).decode("utf-8").strip("=")
+
+
+def setup_hotspot_and_client_for_upstream_type(
+    server_device: android_device,
+    client_device: android_device,
+    upstream_type: UpstreamType,
+) -> (str, int):
+  """Setup the hotspot with a connected client with the specified upstream type.
+
+  This creates a hotspot, make the client connect
+  to it, and verify the packet is forwarded by the hotspot.
+  And returns interface name of both if successful.
+  """
+  server = server_device.connectivity_multi_devices_snippet
+  client = client_device.connectivity_multi_devices_snippet
+
+  # Assert pre-conditions specific to each upstream type.
+  asserts.skip_if(not client.hasWifiFeature(), "Client requires Wifi feature")
+  asserts.skip_if(
+      not server.hasHotspotFeature(), "Server requires hotspot feature"
+  )
+  if upstream_type == UpstreamType.CELLULAR:
+    asserts.skip_if(
+        not server.hasTelephonyFeature(), "Server requires Telephony feature"
+    )
+    server.requestCellularAndEnsureDefault()
+  elif upstream_type == UpstreamType.WIFI:
+    asserts.skip_if(
+        not server.isStaApConcurrencySupported(),
+        "Server requires Wifi AP + STA concurrency",
+    )
+    server.ensureWifiIsDefault()
+  else:
+    raise ValueError(f"Invalid upstream type: {upstream_type}")
+
+  # Generate ssid/passphrase with random characters to make sure nearby devices won't
+  # connect unexpectedly. Note that total length of ssid cannot go over 32.
+  test_ssid = "HOTSPOT-" + generate_uuid32_base64()
+  test_passphrase = generate_uuid32_base64()
+
+  # Create a hotspot with fixed SSID and password.
+  hotspot_interface = server.startHotspot(test_ssid, test_passphrase)
+
+  # Make the client connects to the hotspot.
+  client_network = client.connectToWifi(test_ssid, test_passphrase)
+
+  return hotspot_interface, client_network
+
+
+def cleanup_tethering_for_upstream_type(
+    server_device: android_device, upstream_type: UpstreamType
+) -> None:
+  server = server_device.connectivity_multi_devices_snippet
+  if upstream_type == UpstreamType.CELLULAR:
+    server.unrequestCellular()
+  # Teardown the hotspot.
+  server.stopAllTethering()