diff --git a/bramble-core/src/test/java/org/briarproject/bramble/versioning/ClientVersioningValidatorTest.java b/bramble-core/src/test/java/org/briarproject/bramble/versioning/ClientVersioningValidatorTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..d13be23405cf1b1e5b2e904e9d52bd64a0adee39
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+++ b/bramble-core/src/test/java/org/briarproject/bramble/versioning/ClientVersioningValidatorTest.java
@@ -0,0 +1,274 @@
+package org.briarproject.bramble.versioning;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.BdfMessageContext;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.data.MetadataEncoder;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.junit.Test;
+
+import static java.util.Collections.emptyList;
+import static org.briarproject.bramble.api.sync.ClientId.MAX_CLIENT_ID_LENGTH;
+import static org.briarproject.bramble.api.versioning.ClientVersioningManager.CLIENT_ID;
+import static org.briarproject.bramble.api.versioning.ClientVersioningManager.MAJOR_VERSION;
+import static org.briarproject.bramble.test.TestUtils.getClientId;
+import static org.briarproject.bramble.test.TestUtils.getGroup;
+import static org.briarproject.bramble.test.TestUtils.getMessage;
+import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
+import static org.briarproject.bramble.util.StringUtils.getRandomString;
+import static org.briarproject.bramble.versioning.ClientVersioningConstants.MSG_KEY_LOCAL;
+import static org.briarproject.bramble.versioning.ClientVersioningConstants.MSG_KEY_UPDATE_VERSION;
+import static org.junit.Assert.assertEquals;
+
+public class ClientVersioningValidatorTest extends BrambleMockTestCase {
+
+	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 ClientVersioningValidator validator =
+			new ClientVersioningValidator(clientHelper, metadataEncoder, clock);
+
+	private final Group group = getGroup(CLIENT_ID, MAJOR_VERSION);
+	private final Message message = getMessage(group.getId());
+	private final ClientId clientId = getClientId();
+
+	@Test(expected = FormatException.class)
+	public void testRejectsTooShortBody() throws Exception {
+		BdfList body = BdfList.of(new BdfList());
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsTooLongBody() throws Exception {
+		BdfList body = BdfList.of(new BdfList(), 123, null);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNullStatesList() throws Exception {
+		BdfList body = BdfList.of(null, 123);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNonListStatesList() throws Exception {
+		BdfList body = BdfList.of("", 123);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test
+	public void testAcceptsEmptyStatesList() throws Exception {
+		BdfList body = BdfList.of(new BdfList(), 123);
+		BdfMessageContext context =
+				validator.validateMessage(message, group, body);
+		assertEquals(emptyList(), context.getDependencies());
+		BdfDictionary expectedMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 123L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		assertEquals(expectedMeta, context.getDictionary());
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNullUpdateVersion() throws Exception {
+		BdfList body = BdfList.of(new BdfList(), null);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNonLongUpdateVersion() throws Exception {
+		BdfList body = BdfList.of(new BdfList(), "123");
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNegativeUpdateVersion() throws Exception {
+		BdfList body = BdfList.of(new BdfList(), -1);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test
+	public void testAcceptsZeroUpdateVersion() throws Exception {
+		BdfList body = BdfList.of(new BdfList(), 0);
+		BdfMessageContext context =
+				validator.validateMessage(message, group, body);
+		assertEquals(emptyList(), context.getDependencies());
+		BdfDictionary expectedMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 0L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		assertEquals(expectedMeta, context.getDictionary());
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsTooShortClientState() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, 234);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsTooLongClientState() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, 234, true, null);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNullClientId() throws Exception {
+		BdfList state = BdfList.of(null, 123, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNonStringClientId() throws Exception {
+		byte[] id = getRandomBytes(MAX_CLIENT_ID_LENGTH);
+		BdfList state = BdfList.of(id, 123, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsTooShortClientId() throws Exception {
+		BdfList state = BdfList.of("", 123, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test
+	public void testAcceptsMinLengthClientId() throws Exception {
+		BdfList state = BdfList.of(getRandomString(1), 123, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		BdfMessageContext context =
+				validator.validateMessage(message, group, body);
+		assertEquals(emptyList(), context.getDependencies());
+		BdfDictionary expectedMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 345L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		assertEquals(expectedMeta, context.getDictionary());
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsTooLongClientId() throws Exception {
+		String id = getRandomString(MAX_CLIENT_ID_LENGTH + 1);
+		BdfList state = BdfList.of(id, 123, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test
+	public void testAcceptsMaxLengthClientId() throws Exception {
+		String id = getRandomString(MAX_CLIENT_ID_LENGTH);
+		BdfList state = BdfList.of(id, 123, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		BdfMessageContext context =
+				validator.validateMessage(message, group, body);
+		assertEquals(emptyList(), context.getDependencies());
+		BdfDictionary expectedMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 345L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		assertEquals(expectedMeta, context.getDictionary());
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNullMajorVersion() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), null, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNonLongMajorVersion() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), "123", 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNegativeMajorVersion() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), -1, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test
+	public void testAcceptsZeroMajorVersion() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 0, 234, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		BdfMessageContext context =
+				validator.validateMessage(message, group, body);
+		assertEquals(emptyList(), context.getDependencies());
+		BdfDictionary expectedMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 345L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		assertEquals(expectedMeta, context.getDictionary());
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNullMinorVersion() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, null, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNonLongMinorVersion() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, "234", true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNegativeMinorVersion() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, -1, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test
+	public void testAcceptsZeroMinorVersion() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, 0, true);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		BdfMessageContext context =
+				validator.validateMessage(message, group, body);
+		assertEquals(emptyList(), context.getDependencies());
+		BdfDictionary expectedMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 345L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		assertEquals(expectedMeta, context.getDictionary());
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNullActiveFlag() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, 234, null);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test(expected = FormatException.class)
+	public void testRejectsNonBooleanActiveFlag() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, 234, "true");
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		validator.validateMessage(message, group, body);
+	}
+
+	@Test
+	public void testAcceptsNegativeActiveFlag() throws Exception {
+		BdfList state = BdfList.of(clientId.getString(), 123, 234, false);
+		BdfList body = BdfList.of(BdfList.of(state), 345);
+		BdfMessageContext context =
+				validator.validateMessage(message, group, body);
+		assertEquals(emptyList(), context.getDependencies());
+		BdfDictionary expectedMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 345L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		assertEquals(expectedMeta, context.getDictionary());
+	}
+}