Add unit test class for EthernetInterfaceStateMachine

This currently just invokes the constructor and does nothing else.
EthernetInterfaceStateMachine does not currently provide a way to
transition out of LinkDownState.

Test: run test
Change-Id: Ica8faced0abe33bb70ec5e3f950bc0af75f78f16
diff --git a/tests/unit/java/com/android/server/ethernet/EthernetInterfaceStateMachineTest.kt b/tests/unit/java/com/android/server/ethernet/EthernetInterfaceStateMachineTest.kt
new file mode 100644
index 0000000..a4657e2
--- /dev/null
+++ b/tests/unit/java/com/android/server/ethernet/EthernetInterfaceStateMachineTest.kt
@@ -0,0 +1,62 @@
+/*
+ * 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.server.ethernet
+
+import android.content.Context
+import android.net.NetworkCapabilities
+import android.net.NetworkProvider
+import android.os.Build
+import android.os.Handler
+import android.os.test.TestLooper
+import androidx.test.filters.SmallTest
+import com.android.testutils.DevSdkIgnoreRule
+import com.android.testutils.DevSdkIgnoreRunner
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.Mock
+import org.mockito.MockitoAnnotations
+
+private const val IFACE = "eth0"
+private val CAPS = NetworkCapabilities.Builder().build()
+
+@SmallTest
+@RunWith(DevSdkIgnoreRunner::class)
+@DevSdkIgnoreRule.IgnoreUpTo(Build.VERSION_CODES.S_V2)
+class EthernetInterfaceStateMachineTest {
+    private val looper = TestLooper()
+    private lateinit var ifaceState: EthernetInterfaceStateMachine
+
+    @Mock private lateinit var context: Context
+    @Mock private lateinit var provider: NetworkProvider
+    @Mock private lateinit var deps: EthernetNetworkFactory.Dependencies
+
+    @Before
+    fun setUp() {
+        MockitoAnnotations.initMocks(this)
+
+        val handler = Handler(looper.looper)
+        ifaceState = EthernetInterfaceStateMachine(IFACE, handler, context, CAPS, provider, deps)
+    }
+
+    // TODO: actually test something.
+    @Test
+    fun doNothing() {
+        assertTrue(true)
+    }
+}