Add unit tests for the NO_METHOD compressor

These required some special-casing, since some of the assumption
about real compression algorithms don't actually hold for the
identity transform.  Specifically, we had assumed:

  - compression functions typically change the lengths of their
    inputs.
  - decompression functions can detect truncated inputs
  - compression functions have detectable headers

None of those is true for the identity transformation.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/test/test_buffers.c b/src/test/test_buffers.c
index ce5ac97b3d..38b0824304 100644
--- a/src/test/test_buffers.c
+++ b/src/test/test_buffers.c
@@ -611,7 +611,11 @@ test_buffers_compress_fin_at_chunk_end_impl(compress_method_t method,
 
   tt_int_op(fetch_from_buf(contents, in_len, buf), OP_EQ, 0);
 
-  tt_uint_op(in_len, OP_GT, headerjunk);
+  if (method == NO_METHOD) {
+    tt_uint_op(in_len, OP_EQ, headerjunk);
+  } else {
+    tt_uint_op(in_len, OP_GT, headerjunk);
+  }
 
   tt_int_op(0, OP_EQ, tor_uncompress(&expanded, &out_len,
                                      contents + headerjunk,
@@ -855,6 +859,8 @@ struct testcase_t buffer_tests[] = {
     &passthrough_setup, (char*)"x-zstd" },
   { "compress/lzma", test_buffers_compress, TT_FORK,
     &passthrough_setup, (char*)"x-lzma" },
+  { "compress/none", test_buffers_compress, TT_FORK,
+    &passthrough_setup, (char*)"identity" },
 
   END_OF_TESTCASES
 };