diff --git a/briar-tests/src/org/briarproject/sync/ValidationManagerImplTest.java b/briar-tests/src/org/briarproject/sync/ValidationManagerImplTest.java
index 4863c85c9abe5ab41d2ec08226c2a417e1e88b9c..b55bacd90694245b784f41b51f083a31c4186516 100644
--- a/briar-tests/src/org/briarproject/sync/ValidationManagerImplTest.java
+++ b/briar-tests/src/org/briarproject/sync/ValidationManagerImplTest.java
@@ -1,14 +1,285 @@
 package org.briarproject.sync;
 
 import org.briarproject.BriarTestCase;
+import org.briarproject.ImmediateExecutor;
+import org.briarproject.TestUtils;
+import org.briarproject.api.UniqueId;
+import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.db.DatabaseComponent;
+import org.briarproject.api.db.Metadata;
+import org.briarproject.api.db.NoSuchGroupException;
+import org.briarproject.api.db.NoSuchMessageException;
+import org.briarproject.api.db.Transaction;
+import org.briarproject.api.event.MessageAddedEvent;
+import org.briarproject.api.sync.ClientId;
+import org.briarproject.api.sync.Group;
+import org.briarproject.api.sync.GroupId;
+import org.briarproject.api.sync.Message;
+import org.briarproject.api.sync.MessageId;
+import org.briarproject.api.sync.MessageValidator;
+import org.briarproject.api.sync.ValidationManager.ValidationHook;
+import org.briarproject.util.ByteUtils;
+import org.jmock.Expectations;
+import org.jmock.Mockery;
 import org.junit.Test;
 
-import static org.junit.Assert.fail;
+import java.util.Arrays;
+import java.util.concurrent.Executor;
 
 public class ValidationManagerImplTest extends BriarTestCase {
 
+	private final ClientId clientId = new ClientId(TestUtils.getRandomId());
+	private final MessageId messageId = new MessageId(TestUtils.getRandomId());
+	private final MessageId messageId1 = new MessageId(TestUtils.getRandomId());
+	private final GroupId groupId = new GroupId(TestUtils.getRandomId());
+	private final byte[] descriptor = new byte[32];
+	private final Group group = new Group(groupId, clientId, descriptor);
+	private final long timestamp = System.currentTimeMillis();
+	private final byte[] raw = new byte[123];
+	private final Message message = new Message(messageId, groupId, timestamp,
+			raw);
+	private final Message message1 = new Message(messageId1, groupId, timestamp,
+			raw);
+	private final Metadata metadata = new Metadata();
+	private final ContactId contactId = new ContactId(234);
+
+	public ValidationManagerImplTest() {
+		// Encode the messages
+		System.arraycopy(groupId.getBytes(), 0, raw, 0, UniqueId.LENGTH);
+		ByteUtils.writeUint64(timestamp, raw, UniqueId.LENGTH);
+	}
+
+	@Test
+	public void testMessagesAreValidatedAtStartup() throws Exception {
+		Mockery context = new Mockery();
+		final DatabaseComponent db = context.mock(DatabaseComponent.class);
+		final Executor dbExecutor = new ImmediateExecutor();
+		final Executor cryptoExecutor = new ImmediateExecutor();
+		final MessageValidator validator = context.mock(MessageValidator.class);
+		final ValidationHook hook = context.mock(ValidationHook.class);
+		final Transaction txn = new Transaction(null);
+		final Transaction txn1 = new Transaction(null);
+		final Transaction txn2 = new Transaction(null);
+		final Transaction txn3 = new Transaction(null);
+		final Transaction txn4 = new Transaction(null);
+		context.checking(new Expectations() {{
+			// Get messages to validate
+			oneOf(db).startTransaction();
+			will(returnValue(txn));
+			oneOf(db).getMessagesToValidate(txn, clientId);
+			will(returnValue(Arrays.asList(messageId, messageId1)));
+			oneOf(db).endTransaction(txn);
+			// Load the first raw message and group
+			oneOf(db).startTransaction();
+			will(returnValue(txn1));
+			oneOf(db).getRawMessage(txn1, messageId);
+			will(returnValue(raw));
+			oneOf(db).getGroup(txn1, groupId);
+			will(returnValue(group));
+			oneOf(db).endTransaction(txn1);
+			// Validate the first message: valid
+			oneOf(validator).validateMessage(message, group);
+			will(returnValue(metadata));
+			// Store the validation result for the first message
+			oneOf(db).startTransaction();
+			will(returnValue(txn2));
+			oneOf(db).mergeMessageMetadata(txn2, messageId, metadata);
+			oneOf(db).setMessageValid(txn2, message, clientId, true);
+			oneOf(db).setMessageShared(txn2, message, true);
+			// Call the hook for the first message
+			oneOf(hook).validatingMessage(txn2, message, clientId, metadata);
+			oneOf(db).endTransaction(txn2);
+			// Load the second raw message and group
+			oneOf(db).startTransaction();
+			will(returnValue(txn3));
+			oneOf(db).getRawMessage(txn3, messageId1);
+			will(returnValue(raw));
+			oneOf(db).getGroup(txn3, groupId);
+			will(returnValue(group));
+			oneOf(db).endTransaction(txn3);
+			// Validate the second message: invalid
+			oneOf(validator).validateMessage(message1, group);
+			will(returnValue(null));
+			// Store the validation result for the second message
+			oneOf(db).startTransaction();
+			will(returnValue(txn4));
+			oneOf(db).setMessageValid(txn4, message1, clientId, false);
+			oneOf(db).endTransaction(txn4);
+		}});
+
+		ValidationManagerImpl vm = new ValidationManagerImpl(db, dbExecutor,
+				cryptoExecutor);
+		vm.registerMessageValidator(clientId, validator);
+		vm.registerValidationHook(hook);
+		vm.start();
+
+		context.assertIsSatisfied();
+	}
+
+	@Test
+	public void testValidationContinuesAfterNoSuchMessageException()
+			throws Exception {
+		Mockery context = new Mockery();
+		final DatabaseComponent db = context.mock(DatabaseComponent.class);
+		final Executor dbExecutor = new ImmediateExecutor();
+		final Executor cryptoExecutor = new ImmediateExecutor();
+		final MessageValidator validator = context.mock(MessageValidator.class);
+		final ValidationHook hook = context.mock(ValidationHook.class);
+		final Transaction txn = new Transaction(null);
+		final Transaction txn1 = new Transaction(null);
+		final Transaction txn2 = new Transaction(null);
+		final Transaction txn3 = new Transaction(null);
+		context.checking(new Expectations() {{
+			// Get messages to validate
+			oneOf(db).startTransaction();
+			will(returnValue(txn));
+			oneOf(db).getMessagesToValidate(txn, clientId);
+			will(returnValue(Arrays.asList(messageId, messageId1)));
+			oneOf(db).endTransaction(txn);
+			// Load the first raw message - *gasp* it's gone!
+			oneOf(db).startTransaction();
+			will(returnValue(txn1));
+			oneOf(db).getRawMessage(txn1, messageId);
+			will(throwException(new NoSuchMessageException()));
+			oneOf(db).endTransaction(txn1);
+			// Load the second raw message and group
+			oneOf(db).startTransaction();
+			will(returnValue(txn2));
+			oneOf(db).getRawMessage(txn2, messageId1);
+			will(returnValue(raw));
+			oneOf(db).getGroup(txn2, groupId);
+			will(returnValue(group));
+			oneOf(db).endTransaction(txn2);
+			// Validate the second message: invalid
+			oneOf(validator).validateMessage(message1, group);
+			will(returnValue(null));
+			// Store the validation result for the second message
+			oneOf(db).startTransaction();
+			will(returnValue(txn3));
+			oneOf(db).setMessageValid(txn3, message1, clientId, false);
+			oneOf(db).endTransaction(txn3);
+		}});
+
+		ValidationManagerImpl vm = new ValidationManagerImpl(db, dbExecutor,
+				cryptoExecutor);
+		vm.registerMessageValidator(clientId, validator);
+		vm.registerValidationHook(hook);
+		vm.start();
+
+		context.assertIsSatisfied();
+	}
+
 	@Test
-	public void testUnitTestsExist() {
-		fail(); // FIXME: Write tests
+	public void testValidationContinuesAfterNoSuchGroupException()
+			throws Exception {
+		Mockery context = new Mockery();
+		final DatabaseComponent db = context.mock(DatabaseComponent.class);
+		final Executor dbExecutor = new ImmediateExecutor();
+		final Executor cryptoExecutor = new ImmediateExecutor();
+		final MessageValidator validator = context.mock(MessageValidator.class);
+		final ValidationHook hook = context.mock(ValidationHook.class);
+		final Transaction txn = new Transaction(null);
+		final Transaction txn1 = new Transaction(null);
+		final Transaction txn2 = new Transaction(null);
+		final Transaction txn3 = new Transaction(null);
+		context.checking(new Expectations() {{
+			// Get messages to validate
+			oneOf(db).startTransaction();
+			will(returnValue(txn));
+			oneOf(db).getMessagesToValidate(txn, clientId);
+			will(returnValue(Arrays.asList(messageId, messageId1)));
+			oneOf(db).endTransaction(txn);
+			// Load the first raw message
+			oneOf(db).startTransaction();
+			will(returnValue(txn1));
+			oneOf(db).getRawMessage(txn1, messageId);
+			will(returnValue(raw));
+			// Load the group - *gasp* it's gone!
+			oneOf(db).getGroup(txn1, groupId);
+			will(throwException(new NoSuchGroupException()));
+			oneOf(db).endTransaction(txn1);
+			// Load the second raw message and group
+			oneOf(db).startTransaction();
+			will(returnValue(txn2));
+			oneOf(db).getRawMessage(txn2, messageId1);
+			will(returnValue(raw));
+			oneOf(db).getGroup(txn2, groupId);
+			will(returnValue(group));
+			oneOf(db).endTransaction(txn2);
+			// Validate the second message: invalid
+			oneOf(validator).validateMessage(message1, group);
+			will(returnValue(null));
+			// Store the validation result for the second message
+			oneOf(db).startTransaction();
+			will(returnValue(txn3));
+			oneOf(db).setMessageValid(txn3, message1, clientId, false);
+			oneOf(db).endTransaction(txn3);
+		}});
+
+		ValidationManagerImpl vm = new ValidationManagerImpl(db, dbExecutor,
+				cryptoExecutor);
+		vm.registerMessageValidator(clientId, validator);
+		vm.registerValidationHook(hook);
+		vm.start();
+
+		context.assertIsSatisfied();
+	}
+
+	@Test
+	public void testNonLocalMessagesAreValidatedWhenAdded() throws Exception {
+		Mockery context = new Mockery();
+		final DatabaseComponent db = context.mock(DatabaseComponent.class);
+		final Executor dbExecutor = new ImmediateExecutor();
+		final Executor cryptoExecutor = new ImmediateExecutor();
+		final MessageValidator validator = context.mock(MessageValidator.class);
+		final ValidationHook hook = context.mock(ValidationHook.class);
+		final Transaction txn = new Transaction(null);
+		final Transaction txn1 = new Transaction(null);
+		context.checking(new Expectations() {{
+			// Load the group
+			oneOf(db).startTransaction();
+			will(returnValue(txn));
+			oneOf(db).getGroup(txn, groupId);
+			will(returnValue(group));
+			oneOf(db).endTransaction(txn);
+			// Validate the message: valid
+			oneOf(validator).validateMessage(message, group);
+			will(returnValue(metadata));
+			// Store the validation result
+			oneOf(db).startTransaction();
+			will(returnValue(txn1));
+			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
+			oneOf(db).setMessageValid(txn1, message, clientId, true);
+			oneOf(db).setMessageShared(txn1, message, true);
+			// Call the hook
+			oneOf(hook).validatingMessage(txn1, message, clientId, metadata);
+			oneOf(db).endTransaction(txn1);
+		}});
+
+		ValidationManagerImpl vm = new ValidationManagerImpl(db, dbExecutor,
+				cryptoExecutor);
+		vm.registerMessageValidator(clientId, validator);
+		vm.registerValidationHook(hook);
+		vm.eventOccurred(new MessageAddedEvent(message, contactId));
+
+		context.assertIsSatisfied();
+	}
+
+	@Test
+	public void testLocalMessagesAreNotValidatedWhenAdded() throws Exception {
+		Mockery context = new Mockery();
+		final DatabaseComponent db = context.mock(DatabaseComponent.class);
+		final Executor dbExecutor = new ImmediateExecutor();
+		final Executor cryptoExecutor = new ImmediateExecutor();
+		final MessageValidator validator = context.mock(MessageValidator.class);
+		final ValidationHook hook = context.mock(ValidationHook.class);
+
+		ValidationManagerImpl vm = new ValidationManagerImpl(db, dbExecutor,
+				cryptoExecutor);
+		vm.registerMessageValidator(clientId, validator);
+		vm.registerValidationHook(hook);
+		vm.eventOccurred(new MessageAddedEvent(message, null));
+
+		context.assertIsSatisfied();
 	}
 }