Fix flaky tests due to shared system property

The system property is shared within JVM, change system property in a
test case might break test cases in another test class. To address the
issue, introduce SystemProperty helper class to back up and restore the
system properties in tests.

Bug: 373177618
Flag: EXEMPT Test only
Test: atest SettingsRoboTests
Change-Id: I15539ce5ac425f35571d796baa25f259df1b601f

tests/robotests/Android.bp

@@ -109,7 +109,10 @@ android_robolectric_test {
 
 java_library {
     name: "Settings-robo-testutils",
-    srcs: ["testutils/**/*.java"],
+    srcs: [
+        "testutils/**/*.java",
+        "testutils/**/*.kt",
+    ],
     libs: [
         "Robolectric_all-target_upstream",
         "Settings-core",

tests/robotests/src/com/android/settings/biometrics/fingerprint/FingerprintEnrollEnrollingTest.java

@@ -63,12 +63,14 @@ import android.widget.TextView;
 
 import com.android.settings.R;
 import com.android.settings.testutils.FakeFeatureFactory;
+import com.android.settings.testutils.SystemProperty;
 import com.android.settings.widget.RingProgressBar;
 
 import com.airbnb.lottie.LottieAnimationView;
 import com.airbnb.lottie.LottieTask;
 import com.google.android.setupdesign.GlifLayout;
 
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Test;
@@ -111,15 +113,23 @@ public class FingerprintEnrollEnrollingTest {
     private final int[] mSfpsStageThresholds = new int[]{0, 9, 13, 19, 25};
     private final int[] mUdfpsStageThresholds = new int[]{0, 13, 17, 22};
 
+    private final SystemProperty mSystemProperty = new SystemProperty();
+
     private FingerprintEnrollEnrolling mActivity;
     private Context mContext;
 
     @Before
     public void setUp() {
         MockitoAnnotations.initMocks(this);
+        mSystemProperty.override("robolectric.createActivityContexts", "true");
         FakeFeatureFactory.setupForTest();
     }
 
+    @After
+    public void tearDown() {
+        mSystemProperty.close();
+    }
+
     @Test
     public void fingerprintUdfpsEnrollSuccessProgress_shouldNotVibrate() {
         initializeActivityFor(TYPE_UDFPS_OPTICAL);
@@ -645,7 +655,6 @@ public class FingerprintEnrollEnrollingTest {
     }
 
     private void createActivity() {
-        System.setProperty("robolectric.createActivityContexts", "true");
         final Bundle savedInstanceState = new Bundle();
         savedInstanceState.putInt(KEY_STATE_PREVIOUS_ROTATION, Surface.ROTATION_90);
 

tests/robotests/src/com/android/settings/display/DisplayScreenTest.kt

@@ -21,9 +21,9 @@ import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.android.internal.widget.LockPatternUtils
 import com.android.settings.flags.Flags
 import com.android.settings.testutils.FakeFeatureFactory
+import com.android.settings.testutils.SystemProperty
 import com.android.settingslib.preference.CatalystScreenTestCase
 import com.google.common.truth.Truth.assertThat
-import org.junit.Ignore
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.mockito.ArgumentMatchers.anyInt
@@ -66,16 +66,16 @@ class DisplayScreenTest : CatalystScreenTestCase() {
         assertThat(preferenceScreenCreator.isAvailable(contextWrapper)).isFalse()
     }
 
-    @Ignore("robolectric.createActivityContexts cause other test failure")
     override fun migration() {
         // avoid UnsupportedOperationException when getDisplay from context
-        System.setProperty("robolectric.createActivityContexts", "true")
+        SystemProperty("robolectric.createActivityContexts", "true").use {
+            val lockPatternUtils =
+                mock<LockPatternUtils> { on { isSecure(anyInt()) } doReturn true }
+            FakeFeatureFactory.setupForTest().securityFeatureProvider.stub {
+                on { getLockPatternUtils(any()) } doReturn lockPatternUtils
+            }
 
-        val lockPatternUtils = mock<LockPatternUtils> { on { isSecure(anyInt()) } doReturn true }
+            super.migration()
-        FakeFeatureFactory.setupForTest().securityFeatureProvider.stub {
-            on { getLockPatternUtils(any()) } doReturn lockPatternUtils
         }
-
-        super.migration()
     }
 }

tests/robotests/testutils/com/android/settings/testutils/SystemProperty.kt

@@ -0,0 +1,64 @@
+/*
+ * 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.
+ */
+
+package com.android.settings.testutils
+
+/**
+ * Helper class to override system properties.
+ *
+ * [System.setProperty] changes the static state in the JVM, which is shared by all tests. Hence,
+ * there is chance that test cases are dependent/interfered due to system property unexpectedly.
+ * This helper class backs up the old properties when invoking [override] and restore the old
+ * properties in [close] to avoid flaky testing.
+ */
+class SystemProperty(overrides: Map<String, String?> = mapOf()) : AutoCloseable {
+    private val oldProperties = mutableMapOf<String, String?>()
+
+    constructor(key: String, value: String?) : this(mapOf(key to value))
+
+    init {
+        override(overrides)
+    }
+
+    fun override(key: String, value: String?) = override(mapOf(key to value))
+
+    fun override(overrides: Map<String, String?>) {
+        // back up system properties for the overrides
+        for (key in overrides.keys) {
+            // only back up the oldest property
+            if (!oldProperties.containsKey(key)) {
+                oldProperties[key] = System.getProperty(key)
+            }
+        }
+        overrides.overrideProperties()
+    }
+
+    override fun close() {
+        // restore the backed up properties
+        oldProperties.overrideProperties()
+        oldProperties.clear()
+    }
+
+    private fun Map<String, String?>.overrideProperties() {
+        for ((key, value) in this) {
+            if (value != null) {
+                System.setProperty(key, value)
+            } else {
+                System.clearProperty(key)
+            }
+        }
+    }
+}