Add DisableConfigSyncTargetPreparer

The TargetPreparer disables DeviceConfig sync before a test module, and
attempts to reset it to its original state afterwards.

It only supports S+ as the associated commands are not available on R-.
The format of commands has also changed in some T branches , so support
legacy format if the newer format is not supported by the device.

Bug: 210377950
Test: atest CtsNetTestCases using the preparer, verify setting set
      during the test.
Change-Id: Iaabaa1050b024e1378ab1cf87a394cc8ebab227b

1 files changed, 61 insertions, 0 deletions

diff --git a/common/testutils/host/com/android/testutils/DisableConfigSyncTargetPreparer.kt b/common/testutils/host/com/android/testutils/DisableConfigSyncTargetPreparer.kt
new file mode 100644
index 00000000..63f05a6c
--- /dev/null
+++ b/common/testutils/host/com/android/testutils/DisableConfigSyncTargetPreparer.kt
@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2021 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.
+ */
+
+package com.android.testutils
+
+import com.android.tradefed.invoker.TestInformation
+import com.android.tradefed.targetprep.BaseTargetPreparer
+
+/**
+ * A target preparer that disables DeviceConfig sync while running a test.
+ *
+ * Without this preparer, tests that rely on stable values of DeviceConfig flags, for example to
+ * test behavior when setting the flag and resetting it afterwards, may flake as the flags may
+ * be synced with remote servers during the test.
+ */
+class DisableConfigSyncTargetPreparer : BaseTargetPreparer() {
+    private var syncDisabledOriginalValue = "none"
+
+    override fun setUp(testInfo: TestInformation) {
+        if (isDisabled) return
+        syncDisabledOriginalValue = readSyncDisabledOriginalValue(testInfo)
+
+        // The setter is the same in current and legacy S versions
+        testInfo.exec("cmd device_config set_sync_disabled_for_tests until_reboot")
+    }
+
+    override fun tearDown(testInfo: TestInformation, e: Throwable?) {
+        if (isTearDownDisabled) return
+        // May fail harmlessly if called before S
+        testInfo.exec("cmd device_config set_sync_disabled_for_tests $syncDisabledOriginalValue")
+    }
+
+    private fun readSyncDisabledOriginalValue(testInfo: TestInformation): String {
+        return when (val reply = testInfo.exec("cmd device_config get_sync_disabled_for_tests")) {
+            "until_reboot", "persistent", "none" -> reply
+            // Reply does not match known modes, try legacy commands used on S and some T builds
+            else -> when (testInfo.exec("cmd device_config is_sync_disabled_for_tests")) {
+                // The legacy command just said "true" for "until_reboot" or "persistent". There is
+                // no way to know which one was used, so just reset to "until_reboot" to be
+                // conservative.
+                "true" -> "until_reboot"
+                else -> "none"
+            }
+        }
+    }
+}
+
+private fun TestInformation.exec(cmd: String) = this.device.executeShellCommand(cmd)
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