Add NetIdManagerTest

Add a simple test to verify that IDs loop correctly, that they skip used
IDs correctly, and throw when there is no remaining ID.

Test: atest com.android.server.NetIdManagerTest
Change-Id: I4c9518c725156d743286e062fd2eec1423a0459e

tests/net/java/com/android/server/NetIdManagerTest.kt

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2019 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.server
+
+import androidx.test.filters.SmallTest
+import androidx.test.runner.AndroidJUnit4
+import com.android.server.NetIdManager.MIN_NET_ID
+import com.android.testutils.ExceptionUtils.ThrowingRunnable
+import com.android.testutils.assertThrows
+import org.junit.Test
+import org.junit.runner.RunWith
+import kotlin.test.assertEquals
+
+@RunWith(AndroidJUnit4::class)
+@SmallTest
+class NetIdManagerTest {
+    @Test
+    fun testReserveReleaseNetId() {
+        val manager = NetIdManager(MIN_NET_ID + 4)
+        assertEquals(MIN_NET_ID, manager.reserveNetId())
+        assertEquals(MIN_NET_ID + 1, manager.reserveNetId())
+        assertEquals(MIN_NET_ID + 2, manager.reserveNetId())
+        assertEquals(MIN_NET_ID + 3, manager.reserveNetId())
+
+        manager.releaseNetId(MIN_NET_ID + 1)
+        manager.releaseNetId(MIN_NET_ID + 3)
+        // IDs only loop once there is no higher ID available
+        assertEquals(MIN_NET_ID + 4, manager.reserveNetId())
+        assertEquals(MIN_NET_ID + 1, manager.reserveNetId())
+        assertEquals(MIN_NET_ID + 3, manager.reserveNetId())
+        assertThrows(IllegalStateException::class.java, ThrowingRunnable { manager.reserveNetId() })
+        manager.releaseNetId(MIN_NET_ID + 5)
+        // Still no ID available: MIN_NET_ID + 5 was not reserved
+        assertThrows(IllegalStateException::class.java, ThrowingRunnable { manager.reserveNetId() })
+        manager.releaseNetId(MIN_NET_ID + 2)
+        // Throwing an exception still leaves the manager in a working state
+        assertEquals(MIN_NET_ID + 2, manager.reserveNetId())
+    }
+}