diff --git a/tests/include/unittest.hh b/tests/include/unittest.hh
index fb1c90d..437ea77 100644
--- a/tests/include/unittest.hh
+++ b/tests/include/unittest.hh
@@ -36,11 +36,17 @@ char const * TEST_CASE;
 
 template<typename T>
 void assert_equals(
+    const char *file,
+    unsigned line,
+    const char *expected_expr,
+    const char *actual_expr,
     T const & expected,
     T const & actual
 ) {
     if (expected != actual) {
         std::cout << "FAILED: " << TEST_CASE << std::endl;
+        std::cout << file << ":" << line << std::endl;
+        std::cout << expected_expr << " == " << actual_expr << std::endl;
         std::cout << "Expected: " << expected << std::endl;
         std::cout << "Actual:   " << actual << std::endl;
         std::exit(1);
@@ -49,18 +55,27 @@ void assert_equals(
 
 
 void assert_equals(
+    const char *file,
+    unsigned line,
+    const char *expected_expr,
+    const char *actual_expr,
     std::uint8_t const * expected,
     std::uint8_t const * actual,
     std::size_t length
 ) {
     if (std::memcmp(expected, actual, length)) {
         std::cout << "FAILED: " << TEST_CASE << std::endl;
+        std::cout << file << ":" << line << std::endl;
+        std::cout << expected_expr << " == " << actual_expr << std::endl;
         print_hex(std::cout << "Expected: ", expected, length) << std::endl;
         print_hex(std::cout << "Actual:   ", actual, length) << std::endl;
         std::exit(1);
     }
 }
 
+#define assert_equals(expected, actual, ...) assert_equals( \
+    __FILE__, __LINE__, #expected, #actual, expected, actual, ##__VA_ARGS__ \
+)
 
 class TestCase  {
 public:
diff --git a/tests/test_axolotl.cpp b/tests/test_axolotl.cpp
index 08de1cf..f268f2a 100644
--- a/tests/test_axolotl.cpp
+++ b/tests/test_axolotl.cpp
@@ -18,9 +18,6 @@
 
 int main() {
 
-{ /* Loopback test case */
-TestCase test_case("Axolotl Loopback 1");
-
 std::uint8_t root_info[] = "Axolotl";
 std::uint8_t ratchet_info[] = "AxolotlRatchet";
 std::uint8_t message_info[] = "AxolotlMessageKeys";
@@ -31,31 +28,35 @@ axolotl::KdfInfo kdf_info = {
     message_info, sizeof(ratchet_info - 1)
 };
 
-axolotl::Session alice(kdf_info);
-axolotl::Session bob(kdf_info);
-
 std::uint8_t random_bytes[] = "0123456789ABDEF0123456789ABCDEF";
 axolotl::Curve25519KeyPair bob_key;
 axolotl::generate_key(random_bytes, bob_key);
 
 std::uint8_t shared_secret[] = "A secret";
 
+{ /* Send/Receive test case */
+TestCase test_case("Axolotl Send/Receive");
+
+axolotl::Session alice(kdf_info);
+axolotl::Session bob(kdf_info);
+
 alice.initialise_as_bob(shared_secret, sizeof(shared_secret) - 1, bob_key);
 bob.initialise_as_alice(shared_secret, sizeof(shared_secret) - 1, bob_key);
 
 std::uint8_t plaintext[] = "Message";
 std::size_t plaintext_length = sizeof(plaintext) - 1;
 
-std::size_t message_length, random_length, actual_length;
+std::size_t message_length, random_length, output_length;
 std::size_t encrypt_length, decrypt_length;
-
-message_length = bob.encrypt_max_output_length(plaintext_length);
-random_length = bob.encrypt_random_length();
-assert_equals(std::size_t(0), random_length);
-actual_length = alice.decrypt_max_plaintext_length(message_length);
 {
+    /* Bob sends Alice a message */
+    message_length = bob.encrypt_max_output_length(plaintext_length);
+    random_length = bob.encrypt_random_length();
+    assert_equals(std::size_t(0), random_length);
+    output_length = alice.decrypt_max_plaintext_length(message_length);
+
     std::uint8_t message[message_length];
-    std::uint8_t actual[actual_length];
+    std::uint8_t output[output_length];
 
     encrypt_length = bob.encrypt(
         plaintext, plaintext_length,
@@ -66,12 +67,108 @@ actual_length = alice.decrypt_max_plaintext_length(message_length);
 
     decrypt_length = alice.decrypt(
         message, message_length,
-        actual, actual_length
+        output, output_length
     );
     assert_equals(plaintext_length, decrypt_length);
-    assert_equals(plaintext, actual, decrypt_length);
+    assert_equals(plaintext, output, decrypt_length);
 }
 
-} /* Loopback test case */
+
+{
+    /* Alice sends Bob a message */
+    message_length = alice.encrypt_max_output_length(plaintext_length);
+    random_length = alice.encrypt_random_length();
+    assert_equals(std::size_t(32), random_length);
+    output_length = bob.decrypt_max_plaintext_length(message_length);
+
+    std::uint8_t message[message_length];
+    std::uint8_t output[output_length];
+    std::uint8_t random[] = "This is a random 32 byte string.";
+
+    encrypt_length = alice.encrypt(
+        plaintext, plaintext_length,
+        random, 32,
+        message, message_length
+    );
+    assert_equals(message_length, encrypt_length);
+
+    decrypt_length = bob.decrypt(
+        message, message_length,
+        output, output_length
+    );
+    assert_equals(plaintext_length, decrypt_length);
+    assert_equals(plaintext, output, decrypt_length);
+}
+
+} /* Send/receive message test case */
+
+{ /* Out of order test case */
+
+TestCase test_case("Axolotl Out of Order");
+
+axolotl::Session alice(kdf_info);
+axolotl::Session bob(kdf_info);
+
+alice.initialise_as_bob(shared_secret, sizeof(shared_secret) - 1, bob_key);
+bob.initialise_as_alice(shared_secret, sizeof(shared_secret) - 1, bob_key);
+
+std::uint8_t plaintext_1[] = "First Message";
+std::size_t plaintext_1_length = sizeof(plaintext_1) - 1;
+
+std::uint8_t plaintext_2[] = "Second Messsage. A bit longer than the first.";
+std::size_t plaintext_2_length = sizeof(plaintext_2) - 1;
+
+std::size_t message_1_length, message_2_length, random_length, output_length;
+std::size_t encrypt_length, decrypt_length;
+
+{
+    /* Alice sends Bob two messages and they arrive out of order */
+    message_1_length = alice.encrypt_max_output_length(plaintext_1_length);
+    random_length = alice.encrypt_random_length();
+    assert_equals(std::size_t(32), random_length);
+
+    std::uint8_t message_1[message_1_length];
+    std::uint8_t random[] = "This is a random 32 byte string.";
+    encrypt_length = alice.encrypt(
+        plaintext_1, plaintext_1_length,
+        random, 32,
+        message_1, message_1_length
+    );
+    assert_equals(message_1_length, encrypt_length);
+
+    message_2_length = alice.encrypt_max_output_length(plaintext_2_length);
+    random_length = alice.encrypt_random_length();
+    assert_equals(std::size_t(0), random_length);
+
+    std::uint8_t message_2[message_2_length];
+    encrypt_length = alice.encrypt(
+        plaintext_2, plaintext_2_length,
+        NULL, 0,
+        message_2, message_2_length
+    );
+    assert_equals(message_2_length, encrypt_length);
+
+    output_length = bob.decrypt_max_plaintext_length(message_2_length);
+    std::uint8_t output_1[output_length];
+    decrypt_length = bob.decrypt(
+        message_2, message_2_length,
+        output_1, output_length
+    );
+    assert_equals(plaintext_2_length, decrypt_length);
+    assert_equals(plaintext_2, output_1, decrypt_length);
+
+    output_length = bob.decrypt_max_plaintext_length(message_1_length);
+    std::uint8_t output_2[output_length];
+    decrypt_length = bob.decrypt(
+        message_1, message_1_length,
+        output_2, output_length
+    );
+
+    assert_equals(plaintext_1_length, decrypt_length);
+    assert_equals(plaintext_1, output_2, decrypt_length);
+}
+
+} /* Out of order test case */
+
 
 }