Add Unit tests for CryptoComponent#hash()

bramble-core/src/test/java/org/briarproject/bramble/crypto/HashTest.java

+package org.briarproject.bramble.crypto;
+
+import org.briarproject.bramble.BrambleTestCase;
+import org.briarproject.bramble.TestSeedProvider;
+import org.briarproject.bramble.TestUtils;
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertFalse;
+
+public class HashTest extends BrambleTestCase {
+
+	private final CryptoComponent crypto;
+
+	private final String label = TestUtils.getRandomString(42);
+	private final byte[] inputBytes = TestUtils.getRandomBytes(123);
+	private final byte[] inputBytes1 = TestUtils.getRandomBytes(234);
+	private final byte[] inputBytes2 = new byte[0];
+
+	public HashTest() {
+		crypto = new CryptoComponentImpl(new TestSeedProvider());
+	}
+
+	@Test
+	public void testIdenticalInputsProduceIdenticalHashes() {
+		byte[] hash1 = crypto.hash(label, inputBytes, inputBytes1, inputBytes2);
+		byte[] hash2 = crypto.hash(label, inputBytes, inputBytes1, inputBytes2);
+		assertArrayEquals(hash1, hash2);
+	}
+
+	@Test
+	public void testDifferentInputsProduceDifferentHashes() {
+		byte[] hash1 = crypto.hash(label, inputBytes, inputBytes1, inputBytes2);
+		byte[] hash2 = crypto.hash(label, inputBytes2, inputBytes1, inputBytes);
+		assertFalse(Arrays.equals(hash1, hash2));
+	}
+
+	@Test
+	public void testDifferentLabelsProduceDifferentHashes() {
+		String label2 = TestUtils.getRandomString(42);
+		byte[] hash1 = crypto.hash(label, inputBytes, inputBytes1, inputBytes2);
+		byte[] hash2 =
+				crypto.hash(label2, inputBytes, inputBytes1, inputBytes2);
+		assertFalse(Arrays.equals(hash1, hash2));
+	}
+
+}