diff --git a/tests/unit/encoding/block-helpers.t.cpp b/tests/unit/encoding/block-helpers.t.cpp
index 2ca1e02..9325851 100644
--- a/tests/unit/encoding/block-helpers.t.cpp
+++ b/tests/unit/encoding/block-helpers.t.cpp
@@ -108,18 +108,43 @@
   std::list<uint8_t> buf3{1, 1, 1, 1};
 
   Block b1 = makeBinaryBlock(100, buf1.data(), buf1.size()); // char* overload
-  Block b2 = makeBinaryBlock(100, buf2, sizeof(buf2));       // uint8_t* overload
-  Block b3 = makeBinaryBlock(100, buf2);                     // span overload
-  Block b4 = makeBinaryBlock(100, buf1.begin(), buf1.end()); // fast encoding (random access iterator)
-  Block b5 = makeBinaryBlock(100, buf3.begin(), buf3.end()); // slow encoding (general iterator)
+  Block b2 = makeBinaryBlock(100, buf2);                     // span overload
+  Block b3 = makeBinaryBlock(100, buf1.begin(), buf1.end()); // fast encoding (random access iterator)
+  Block b4 = makeBinaryBlock(100, buf3.begin(), buf3.end()); // slow encoding (general iterator)
 
   BOOST_CHECK_EQUAL(b1, b2);
   BOOST_CHECK_EQUAL(b1, b3);
   BOOST_CHECK_EQUAL(b1, b4);
-  BOOST_CHECK_EQUAL(b1, b5);
   BOOST_CHECK_EQUAL(b1.type(), 100);
   BOOST_CHECK_EQUAL(b1.value_size(), buf1.size());
   BOOST_CHECK_EQUAL_COLLECTIONS(b1.value_begin(), b1.value_end(), buf2, buf2 + sizeof(buf2));
+
+  EncodingEstimator estimator;
+  size_t length = prependBinaryBlock(estimator, 100, buf2);
+  BOOST_CHECK_EQUAL(length, 6);
+
+  EncodingBuffer encoder(length, 0);
+  BOOST_CHECK_EQUAL(prependBinaryBlock(encoder, 100, buf2), 6);
+  BOOST_CHECK_EQUAL(encoder.block(), b1);
+}
+
+BOOST_AUTO_TEST_CASE(PrependBlock)
+{
+  EncodingEstimator estimator;
+  Block b1({0x01, 0x03, 0x00, 0x00, 0x00});
+  size_t length = prependBlock(estimator, b1);
+  BOOST_CHECK_EQUAL(length, 5);
+  Block b2(100, b1);
+  length += prependBlock(estimator, b2);
+  BOOST_CHECK_EQUAL(length, 12);
+
+  EncodingBuffer encoder(length, 0);
+  BOOST_CHECK_EQUAL(prependBlock(encoder, b1), 5);
+  BOOST_CHECK_EQUAL(prependBlock(encoder, b2), 7);
+  BOOST_CHECK_EQUAL(encoder.size(), 12);
+  encoder.prependVarNumber(encoder.size());
+  encoder.prependVarNumber(200);
+  BOOST_CHECK_EQUAL(encoder.block(), "C80C 64050103000000 0103000000"_block);
 }
 
 BOOST_AUTO_TEST_CASE(Nested)