diff --git a/briar-tests/src/org/briarproject/messaging/PrivateMessageValidatorTest.java b/briar-tests/src/org/briarproject/messaging/PrivateMessageValidatorTest.java
index 28668520ff6ba9a821226a93e24d50cc4131494c..f73d02f966ec80524cad7d18c97d45448b85d7e8 100644
--- a/briar-tests/src/org/briarproject/messaging/PrivateMessageValidatorTest.java
+++ b/briar-tests/src/org/briarproject/messaging/PrivateMessageValidatorTest.java
@@ -1,14 +1,116 @@
 package org.briarproject.messaging;
 
 import org.briarproject.BriarTestCase;
+import org.briarproject.TestUtils;
+import org.briarproject.api.FormatException;
+import org.briarproject.api.clients.BdfMessageContext;
+import org.briarproject.api.clients.ClientHelper;
+import org.briarproject.api.data.BdfDictionary;
+import org.briarproject.api.data.BdfList;
+import org.briarproject.api.data.MetadataEncoder;
+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.system.Clock;
+import org.jmock.Mockery;
+import org.junit.After;
 import org.junit.Test;
 
-import static org.junit.Assert.fail;
+import static org.briarproject.api.messaging.MessagingConstants.MAX_PRIVATE_MESSAGE_BODY_LENGTH;
+import static org.briarproject.clients.BdfConstants.MSG_KEY_READ;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 
 public class PrivateMessageValidatorTest extends BriarTestCase {
 
+	private final Mockery context = new Mockery();
+	private final ClientHelper clientHelper = context.mock(ClientHelper.class);
+	private final MetadataEncoder metadataEncoder =
+			context.mock(MetadataEncoder.class);
+	private final Clock clock = context.mock(Clock.class);
+
+	private final MessageId messageId = new MessageId(TestUtils.getRandomId());
+	private final GroupId groupId = new GroupId(TestUtils.getRandomId());
+	private final long timestamp = 1234567890 * 1000L;
+	private final byte[] raw = TestUtils.getRandomBytes(123);
+	private final Message message =
+			new Message(messageId, groupId, timestamp, raw);
+	private final ClientId clientId =
+			new ClientId(TestUtils.getRandomString(123));
+	private final byte[] descriptor = TestUtils.getRandomBytes(123);
+	private final Group group = new Group(groupId, clientId, descriptor);
+
+	@After
+	public void checkExpectations() {
+		context.assertIsSatisfied();
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsEmptyBody() throws Exception {
+		PrivateMessageValidator v = new PrivateMessageValidator(clientHelper,
+				metadataEncoder, clock);
+		v.validateMessage(message, group, new BdfList());
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsTooLongBody() throws Exception {
+		PrivateMessageValidator v = new PrivateMessageValidator(clientHelper,
+				metadataEncoder, clock);
+		v.validateMessage(message, group, BdfList.of("", ""));
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNullContent() throws Exception {
+		PrivateMessageValidator v = new PrivateMessageValidator(clientHelper,
+				metadataEncoder, clock);
+		v.validateMessage(message, group, BdfList.of((String) null));
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNonStringContent() throws Exception {
+		PrivateMessageValidator v = new PrivateMessageValidator(clientHelper,
+				metadataEncoder, clock);
+		v.validateMessage(message, group, BdfList.of(123));
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsTooLongContent() throws Exception {
+		PrivateMessageValidator v = new PrivateMessageValidator(clientHelper,
+				metadataEncoder, clock);
+		String content =
+				TestUtils.getRandomString(MAX_PRIVATE_MESSAGE_BODY_LENGTH + 1);
+		v.validateMessage(message, group, BdfList.of(content));
+	}
+
 	@Test
-	public void testUnitTestsExist() {
-		fail(); // FIXME: Write tests
+	public void testAcceptsMaxLengthContent() throws Exception {
+		PrivateMessageValidator v = new PrivateMessageValidator(clientHelper,
+				metadataEncoder, clock);
+		String content =
+				TestUtils.getRandomString(MAX_PRIVATE_MESSAGE_BODY_LENGTH);
+		BdfMessageContext context =
+				v.validateMessage(message, group, BdfList.of(content));
+		assertExpectedContext(context);
+	}
+
+	@Test
+	public void testAcceptsEmptyContent() throws Exception {
+		PrivateMessageValidator v = new PrivateMessageValidator(clientHelper,
+				metadataEncoder, clock);
+		BdfMessageContext context =
+				v.validateMessage(message, group, BdfList.of(""));
+		assertExpectedContext(context);
+	}
+
+	private void assertExpectedContext(BdfMessageContext context)
+			throws FormatException {
+		assertEquals(0, context.getDependencies().size());
+		BdfDictionary meta = context.getDictionary();
+		assertEquals(3, meta.size());
+		assertEquals(Long.valueOf(timestamp), meta.getLong("timestamp"));
+		assertFalse(meta.getBoolean("local"));
+		assertFalse(meta.getBoolean(MSG_KEY_READ));
 	}
 }