Add unittest for lz4diff postfix feature

Test: th
Bug: 206729162

Change-Id: If2e9446fbb04e9bb264ed8101fb761a6c591d23a
diff --git a/lz4diff/lz4diff_compress.cc b/lz4diff/lz4diff_compress.cc
index 333148a..e580c91 100644
--- a/lz4diff/lz4diff_compress.cc
+++ b/lz4diff/lz4diff_compress.cc
@@ -40,8 +40,7 @@
     compressed_size += block.compressed_length;
   }
   CHECK_EQ(uncompressed_size, blob.size());
-  Blob output;
-  output.resize(utils::RoundUp(compressed_size, kBlockSize));
+  Blob output(utils::RoundUp(compressed_size, kBlockSize));
   auto hc = LZ4_createStreamHC();
   DEFER {
     if (hc) {
@@ -110,10 +109,6 @@
                   0);
       }
     }
-    if (static_cast<uint64_t>(src_size) != block.uncompressed_length) {
-      LOG(WARNING) << "Recompress size mismatch: " << src_size << ", "
-                   << block.uncompressed_length;
-    }
   }
   // Any trailing data will be copied to the output buffer.
   output.insert(output.end(), blob.begin() + uncompressed_size, blob.end());