WalletAppKit: call awaitTerminated() in close()

This adds basic unit tests.

core/src/main/java/org/bitcoinj/kits/WalletAppKit.java

@@ -571,9 +571,13 @@ public class WalletAppKit extends AbstractIdleService implements Closeable {
         }
     }
 
+    /**
+     * Close and release resources. Implements {@link Closeable}. This should be idempotent.
+     */
     @Override
     public void close() {
         stopAsync();
+        awaitTerminated();
     }
 
     public BitcoinNetwork network() {

core/src/test/java/org/bitcoinj/kits/WalletAppKitTest.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright by the original author or authors.
+ *
+ * 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 org.bitcoinj.kits;
+
+import org.bitcoinj.base.ScriptType;
+import org.bitcoinj.wallet.KeyChainGroupStructure;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.IOException;
+
+import static org.bitcoinj.base.BitcoinNetwork.REGTEST;
+import static org.bitcoinj.base.ScriptType.P2WPKH;
+import static org.bitcoinj.wallet.KeyChainGroupStructure.BIP43;
+
+/**
+ * Test WalletAppKit
+ */
+public class WalletAppKitTest {
+    @Rule
+    public TemporaryFolder tmpFolder = new TemporaryFolder();
+    static final String filePrefix = "UnitTestWalletAppKit";
+
+    @Test
+    public void constructAndClose() throws IOException {
+        WalletAppKit kit = new WalletAppKit(REGTEST, P2WPKH, BIP43, tmpFolder.newFolder(), filePrefix);
+        kit.close();
+    }
+
+    @Test
+    public void constructAndCloseTwice() throws IOException {
+        WalletAppKit kit = new WalletAppKit(REGTEST, P2WPKH, BIP43, tmpFolder.newFolder(), filePrefix);
+        kit.close();
+        kit.close();
+    }
+
+    @Test
+    public void launchAndClose() throws IOException {
+        WalletAppKit kit = WalletAppKit.launch(REGTEST, tmpFolder.newFolder(), filePrefix);
+        kit.close();
+    }
+
+    @Test
+    public void launchAndCloseTwice() throws IOException {
+        WalletAppKit kit = WalletAppKit.launch(REGTEST, tmpFolder.newFolder(), filePrefix);
+        kit.close();
+        kit.close();
+    }
+}