tests: mine to height before checking sync notifications

### src/test/java/TestMoneroWalletFull.java
@@ -666,37 +666,23 @@ private void testSyncSeed(Long startHeight, Long restoreHeight, boolean skipGtCo
       if (testPostSyncNotifications) {
         
         // start automatic syncing
+        long walletHeight = wallet.getHeight();
         wallet.startSyncing(TestUtils.SYNC_PERIOD_IN_MS);
         
-        // attempt to start mining to push the network along  // TODO: TestUtils.tryStartMining() : reqId, TestUtils.tryStopMining(reqId)
-        boolean startedMining = false;
-        try {
-          StartMining.startMining();
-          startedMining = true;
-        } catch (Exception e) {
-          // no problem
-        }
-        
+        System.out.println("Waiting for next block to test post sync notifications");
+        StartMining.mineToHeight(walletHeight + 1);
+
+        // ensure wallet has time to detect new block
         try {
-          
-          // wait for block
-          System.out.println("Waiting for next block to test post sync notifications");
-          daemon.waitForNextBlockHeader();
-          
-          // ensure wallet has time to detect new block
-          try {
-            TimeUnit.MILLISECONDS.sleep(TestUtils.SYNC_PERIOD_IN_MS + 3000); // sleep for wallet interval + time to sync
-          } catch (InterruptedException e) {
-            e.printStackTrace();
-            throw new RuntimeException(e.getMessage());
-          }
-          
-          // test that wallet listener's onSyncProgress() and onNewBlock() were invoked after previous completion
-          assertTrue(walletSyncTester.getOnSyncProgressAfterDone());
-          assertTrue(walletSyncTester.getOnNewBlockAfterDone());
-        } finally {
-          if (startedMining) wallet.stopMining();
+          TimeUnit.MILLISECONDS.sleep(TestUtils.SYNC_PERIOD_IN_MS + 3000); // sleep for wallet interval + time to sync
+        } catch (InterruptedException e) {
+          e.printStackTrace();
+          throw new RuntimeException(e.getMessage());
         }
+
+        // test that wallet listener's onSyncProgress() and onNewBlock() were invoked after previous completion
+        assertTrue(walletSyncTester.getOnSyncProgressAfterDone());
+        assertTrue(walletSyncTester.getOnNewBlockAfterDone());
       }
     } finally {
       if (walletGt != null) walletGt.close(true);

### src/test/java/utils/StartMining.java
@@ -1,5 +1,8 @@
 package utils;
 
+import common.utils.GenUtils;
+import monero.daemon.MoneroDaemon;
+
 /**
  * Utility class to start mining.
  */
@@ -8,6 +11,23 @@ public class StartMining {
   public static void main(String[] args) {
     startMining();
   }
+
+  public static void mineToHeight(long height) {
+    MoneroDaemon daemon = TestUtils.getDaemonRpc();
+    if (daemon.getHeight() >= height) return;
+    boolean startedMining = false;
+    if (!daemon.getMiningStatus().isActive()) {
+      try {
+        startMining();
+        startedMining = true;
+      } catch (Exception e) { }
+    }
+    try {
+      while (daemon.getHeight() < height) GenUtils.waitFor(TestUtils.SYNC_PERIOD_IN_MS);
+    } finally {
+      if (startedMining) daemon.stopMining();
+    }
+  }
   
   public static void startMining() {
     startMining(1);