1 Guide

1.1 Introduction

The extfs filesystem is composed of various helpers (uzip, urar, uarc, …). One command every helper must answer to is “list”, to list the files on its filesystem.

The purpose of this tester is to test this “list” facet of every helper to ensure that it indeed works, at present, and that we won’t inadvertently break it, in the future, as we modify its code or MC’s code.

1.2 Key concept: Inputs

Most helpers work by parsing the output of some 3’rd party software. Which for them becomes the input. Helpers sometimes support several variations of such input. E.g., the uzip helper supports three variations.

The tester keeps a repository, in the data folder, of the various inputs each helper proclaims to support. Each input is stored in a file with an .input suffix.

1.3 Key concept: Outputs

Along with each input file, the data folder also holds the output the helper is expected to produce given the corresponding input. Each output is stored in a file with an .output suffix.

We call this output “the expected output”.

Incidentally, an .output file stores not the raw output of the helper but its output after parsing. In other words, what’s stored is the unambiguous meaning of the helper’s output. This means that as long as the helper’s code isn’t modified in a way that changes the meaning of its output, the .output file remains up-to-date.

1.4 How the tester works

The tester feeds each helper its prepared inputs and reads back the helper’s “list” answer — the helper’s output. This output is a list of files in a format similar to ls -l, which MC is able to parse. The tester checks that this output parses without errors (errors are, for example, dates in unsupported format). It then compares this parsed output (which we call “the actual output”) with a previously saved copy of this output which is known to be correct (and which we call “the expected output”, mentioned in the previous section). This previously stored output too is in the data folder, in files with .output suffix.

If there’s any discrepancy between the actual output and the expected output, the test fails.

1.5 Running the tester

You can run the tester with make check.

But you’ll find it more appealing to run the tester with the run script. You’ll get a colorful description of what’s going on.

(run is created by running make check for the 1st time, in the build tree.)

2 Reference

2.1 The data folder

There are several types of files in the data folder:

2.1.1 Input file

An input file is named:


You create such files simply by redirecting the 3’rd party software’s output to a file.

2.1.2 Output file

This file is named the same as the corresponding input file but with an .output suffix.

The easiest way to create these files is by invoking the run script with the --create-output option.

2.1.3 Environment file

Optional. This file defines environment variables the helper may use to determine the variant of the input. This file is named the same as the corresponding input file but with an .env_var suffix.

2.1.4 Arguments file

Optional. This file defines extra command-line options to pass to the parser. This file is named the same as the corresponding input file but with an .args suffix.

The contents of an output file must be the same no matter on what computer and at what time we generate it. Therefore we need to tell the parser to drop any non-fixed elements in that file. E.g., if the dates used are relative (as is the case for the default ls dates), we need to drop them with --drop-mtime. Similarly, if a helper returns user and group names that are different than the running user’s, they must be dropped with --drop-ids.

2.1.5 Other files

Any other file is ignored by the tester.

2.2 mc_parse_ls_l

This program (built with make check) is at the heart of the tester mechanism. It parses a list of files, in a format similar to ls -l, just as MC would. This program is used to parse (and thereby verify) the output of the helpers. You don’t need to invoke it yourself; but, for educational purpose, here are a few examples:

$ LC_ALL=C ls -l | ./mc_parse_ls_l

$ LC_ALL=C ls -l | ./mc_parse_ls_l --symbolic-ids

$ LC_ALL=C ls -l | ./mc_parse_ls_l --output-format yaml

2.3 test_all

This is the tester itself. You invoke it with make check, or with the run script. Invoking it directly is a bit involving because you need to provide it with 2 or 3 directory paths. run does this work for you.


When a helper runs under the tester, the environment variable MC_TEST_EXTFS_LIST_CMD holds the command that’s to provide input. The helper’s source code must be modified to use this command instead of the command it usually uses. This is the device which lets us plug our own input into the helper and without which a helper can’t be tested!

Let’s have a little example. The uzoo helper originally has:

mczoofs_list () {
  $ZOO lq "$ARCHIVE" | mawk '......'

To make this helper testable, we need to change the first line to:


(or equivalent.)

The command in MC_TEST_EXTFS_LIST_CMD is a black-box for the helper, and it intentionally ignores any arguments passed to it (so that lq "$ARCHIVE", above, won’t cause problems).