ethernet: clean up EthernetManagerTest

createChangeEvent is not expected to be called from a test, so make it
private. Also delete pollOrThrow as polling inline creates a better log
output.

Test: atest EthernetManagerTest
Change-Id: I2399960fee2c51fdf340186189ae83a20c4ac6f3

tests/cts/net/src/android/net/cts/EthernetManagerTest.kt

@@ -92,7 +92,6 @@ import kotlin.test.assertFalse
 import kotlin.test.assertNotNull
 import kotlin.test.assertNull
 import kotlin.test.assertTrue
-import kotlin.test.fail
 import org.junit.After
 import org.junit.Assume.assumeFalse
 import org.junit.Assume.assumeTrue
@@ -254,7 +253,7 @@ class EthernetManagerTest {
         }
 
         fun <T : CallbackEntry> expectCallback(expected: T): T {
-            val event = pollOrThrow()
+            val event = events.poll(TIMEOUT_MS)
             assertEquals(expected, event)
             return event as T
         }
@@ -267,14 +266,10 @@ class EthernetManagerTest {
             expectCallback(EthernetStateChanged(state))
         }
 
-        fun createChangeEvent(iface: String, state: Int, role: Int) =
+        private fun createChangeEvent(iface: String, state: Int, role: Int) =
                 InterfaceStateChanged(iface, state, role,
                         if (state != STATE_ABSENT) DEFAULT_IP_CONFIGURATION else null)
 
-        fun pollOrThrow(): CallbackEntry {
-            return events.poll(TIMEOUT_MS) ?: fail("Did not receive callback after ${TIMEOUT_MS}ms")
-        }
-
         fun eventuallyExpect(expected: CallbackEntry) {
             val cb = events.poll(TIMEOUT_MS) { it == expected }
             assertNotNull(cb, "Never received expected $expected. Received: ${events.backtrace()}")