btrfs-progs: add initial tests/README

Signed-off-by: David Sterba <dsterba@suse.com>

tests/README.md

@@ -0,0 +1,136 @@
+# Btrfs-progs tests
+
+Run the tests from the top directory:
+
+```shell
+$ make test
+$ make test-fsck
+$ make test-convert
+```
+
+or selectively from the `tests/` directory:
+
+```shell
+$ ./fsck-tests.sh
+$ ./misc-tests.sh
+```
+
+The verbose output of the tests is logged into a file named after the test
+category, eg. `fsck-tests-results.txt`.
+
+## Selective testing
+
+The test are prefixed by a number for ordering and uniquenes. To run a
+particular test use:
+
+```shell
+$ make TEST=MASK test
+```
+
+where `MASK` is a glob expression that will execute only tests
+that match the MASK. Here the test number comes handy:
+
+```shell
+$ make TEST=001\* test-fsck
+$ TEST=001\* ./fsck-tests.sh
+```
+
+will run the first test in fsck-tests subdirectory.
+
+
+## Test structure
+
+*tests/fsck-tests/:*
+
+  * tests targeted at bugs that are fixable by fsck
+
+*tests/convert-tests/:*
+
+  * coverage tests of ext2/3/4 and btrfs-convert options
+
+*tests/fuzz-tests/:*
+
+  * collection of fuzzed or crafted images
+  * tests that are supposed to run various utilities on the images and not
+    crash
+
+*tests/misc-tests/:*
+
+  * anything that does not fit to the above, the test driver script will only
+    execute `./test.sh` in the test directory
+
+*tests/common:*
+
+  * script with helpers
+
+*tests/test.img:*
+
+  * default testing image, the file is never deleted by the scripts but
+    truncated to 0 bytes, so it keeps it's permissions. It's eg. possible to
+    host it on NFS, make it `chmod a+w` for root.
+
+
+## Other tuning, environment variables
+
+### Instrumentation
+
+It's possible to wrap the tested commands to utilities that might do more
+checking or catch failures at runtime. This can be done by setting the
+`INSTRUMENT` environment variable:
+
+```shell
+INSTRUMENT=valgrind ./fuzz-tests.sh    # in tests/
+make INSTRUMENT=valgrind test-fuzz     # in the top directory
+```
+
+The variable is prepended to the command *unquoted*, all sorts of shell tricks
+are possible.
+
+Note: instrumentation is not applied to privileged commands (anything that uses
+the root helper).
+
+### Verbosity
+
+Setting the variable `TEST_LOG=tty` will print all commands executed by some of
+the wrappers (`run_check` etc), other commands are silent.
+
+### Permissions
+
+Some commands require root privileges (to mount/umount, access loop devices).
+It is assumed that `sudo` will work in some way (no password, password asked
+and cached). Note that instrumentation is not applied in this case, for safety
+reasons. You need to modify the test script instead.
+
+### Cleanup
+
+The tests are supposed to cleanup after themselves if they pass. In case of
+failure, the rest of the tests are skipped and intermediate files, mounts and
+loop devices are kept. This should help to investigate the test failure but at
+least the mounts and loop devices need to be cleaned before the next run.
+
+This is partially done by the script `clean-tests.sh`, you may want to check
+the loop devices as they are managed on a per-test basis.
+
+## New test
+
+1. Pick the category for the new test or fallback to `misc-tests` if not sure. For
+an easy start copy an existing `test.sh` script from some test that might be
+close to the purpose of your new test.
+
+* Use the highest unused number in the sequence, write a short descriptive title
+and join by dashes `-`.
+
+* Write a short description of the bug and how it's teste to the comment at the
+begining of `test.sh`.
+
+* Write the test commands, comment anything that's not obvious.
+
+* Test your test. Use the `TEST` variable to jump right to your test:
+```shell
+$ make TEST=012\* tests-misc           # from top directory
+$ TEST=012\* ./misc-tests.sh           # from tests/
+```
+
+* The commit changelog should reference a commit that either introduced or
+  fixed the bug (or both). Subject line of the shall mention the name of the
+  new directory for ease of search, eg. `btrfs-progs: tests: add 012-subvolume-sync-must-wait`