Running tests

Unit-tests

The unit tests are defined using the googletest and rapidcheck frameworks.

Source and header layout

An example of some files, demonstrating much of what is described below

…
├── src
│   ├── libexpr
│   │   ├── …
│   │   ├── value
│   │   │   ├── context.cc
│   │   │   └── context.hh
│   …   …
├── tests
│   …
│   └── unit
│       ├── libcmd
│       │   └── args.cc
│       ├── libexpr
│       │   ├── …
│       │   └── value
│       │       ├── context.cc
│       │       └── print.cc
│       ├── libexpr-support
│       │   └── tests
│       │       ├── libexpr.hh
│       │       └── value
│       │           ├── context.cc
│       │           └── context.hh
│       ├── libstore
│       │   ├── common-protocol.cc
│       │   ├── data
│       │   │   ├── libstore
│       │   │   │   ├── common-protocol
│       │   │   │   │   ├── content-address.bin
│       │   │   │   │   ├── drv-output.bin
…       …   …   …   …   …

The unit tests for each Lix library (liblixexpr, liblixstore, etc..) live inside a directory src/${library_shortname}/tests within the directory for the library (src/${library_shortname}).

The data is in tests/unit/LIBNAME/data/LIBNAME, with one subdir per library, with the same name as where the code goes. For example, liblixstore code is in src/libstore, and its test data is in tests/unit/libstore/data/libstore. The path to the unit test data directory is passed to the unit test executable with the environment variable _NIX_TEST_UNIT_DATA.

Running tests

You can run the whole testsuite with just test (see justfile for exact invocation of meson), and if you want to run just one test suite, use just test --suite installcheck functional-init where installcheck is the name of the test suite in this case and functional-init is the name of the test.

To get a list of tests, use meson test -C build --list (or just test --list for short).

For installcheck specifically, first run just install before running the test suite (this is due to meson limitations that don't let us put a dependency on installing before doing the test).

Finer-grained filtering within a test suite is also possible using the --gtest_filter command-line option to a test suite executable, or the GTEST_FILTER environment variable.

Unit test support libraries

There are headers and code which are not just used to test the library in question, but also downstream libraries. For example, we do [property testing] with the rapidcheck library. This requires writing Arbitrary "instances", which are used to describe how to generate values of a given type for the sake of running property tests. Because types contain other types, Arbitrary "instances" for some type are not just useful for testing that type, but also any other type that contains it. Downstream types frequently contain upstream types, so it is very important that we share arbitrary instances so that downstream libraries' property tests can also use them.

It is important that these testing libraries don't contain any actual tests themselves. On some platforms they would be run as part of every test executable that uses them, which is redundant. On other platforms they wouldn't be run at all.

Characterization testing

See below for a broader discussion of characterization testing.

Like with the functional characterization, _NIX_TEST_ACCEPT=1 is also used. For example:

$ _NIX_TEST_ACCEPT=1 just test --suite check libstore-unit-tests
...
../tests/unit/libstore/common-protocol.cc:27: Skipped
Cannot read golden master because another test is also updating it

../tests/unit/libstore/common-protocol.cc:62: Skipped
Updating golden master

../tests/unit/libstore/common-protocol.cc:27: Skipped
Cannot read golden master because another test is also updating it

../tests/unit/libstore/common-protocol.cc:62: Skipped
Updating golden master
...

will regenerate the "golden master" expected result for the liblixstore characterization tests. The characterization tests will mark themselves "skipped" since they regenerated the expected result instead of actually testing anything.

Functional tests

The functional tests reside under the tests/functional directory and are listed in tests/functional/meson.build. Each test is a bash script.

Running the whole test suite

Debugging failing functional tests

When a functional test fails, it usually does so somewhere in the middle of the script.

To figure out what's wrong, it is convenient to run the test regularly up to the failing nix command, and then run that command with a debugger like GDB.

For example, if the script looks like:

foo
nix blah blub
bar

edit it like so:

 foo
-nix blah blub
+gdb --args nix blah blub
 bar

Then, running the test with ./mk/debug-test.sh will drop you into GDB once the script reaches that point:

$ ./mk/debug-test.sh tests/functional/${testName}.sh
...
+ gdb blash blub
GNU gdb (GDB) 12.1
...
(gdb)

One can debug the Nix invocation in all the usual ways. For example, enter run to start the Nix invocation.

Characterization testing

Occasionally, Lix utilizes a technique called Characterization Testing as part of the functional tests. This technique is to include the exact output/behavior of a former version of Nix in a test in order to check that Lix continues to produce the same behavior going forward.

For example, this technique is used for the language tests, to check both the printed final value if evaluation was successful, and any errors and warnings encountered.

It is frequently useful to regenerate the expected output. To do that, rerun the failed test(s) with _NIX_TEST_ACCEPT=1. For example:

_NIX_TEST_ACCEPT=1 just test --suite installcheck -v functional-lang

An interesting situation to document is the case when these tests are "overfitted". The language tests are, again, an example of this. The expected successful output of evaluation is supposed to be highly stable – we do not intend to make breaking changes to (the stable parts of) the Nix language. However, the errors and warnings during evaluation (successful or not) are not stable in this way. We are free to change how they are displayed at any time.

It may be surprising that we would test non-normative behavior like diagnostic outputs. Diagnostic outputs are indeed not a stable interface, but they still are important to users. By recording the expected output, the test suite guards against accidental changes, and ensure the result (not just the code that implements it) of the diagnostic code paths are under code review. Regressions are caught, and improvements always show up in code review.

To ensure that characterization testing doesn't make it harder to intentionally change these interfaces, there always must be an easy way to regenerate the expected output, as we do with _NIX_TEST_ACCEPT=1.

Integration tests

The integration tests are defined in the Nix flake under the hydraJobs.tests attribute. These tests include everything that needs to interact with external services or run Lix in a non-trivial distributed setup. Because these tests are expensive and require more than what the standard github-actions setup provides, they only run on the master branch (on https://hydra.nixos.org/jobset/nix/master).

You can run them manually with nix build .#hydraJobs.tests.{testName} or nix-build -A hydraJobs.tests.{testName}

Magic environment variables

FIXME: maybe this section should be moved elsewhere or turned partially into user docs, but I just need a complete index for now. I actually want to ban people calling getenv without writing documentation, and produce a comprehensive list of env-vars used by Lix and enforce it.

This is a non-exhaustive list of almost all environment variables, magic or not, accepted or used by various parts of the test suite as well as Lix itself. Please add more if you find them.

I looked for these in the testsuite with the following bad regexes:

rg '(?:[^A-Za-z]|^)(_[A-Z][^-\[ }/:");$(]+)' -r '$1' --no-filename --only-matching tests | sort -u > vars.txt
rg '\$\{?([A-Z][^-\[ }/:");]+)' -r '$1' --no-filename --only-matching tests | sort -u > vars.txt

I grepped src/ for get[eE]nv\(" to find the mentions in Lix code.

Used by Lix testing support code

• _NIX_TEST_ACCEPT (optional) - Writes out the result of a characterization test as the new expected value. Expected value: 1

• _NIX_TEST_UNIT_DATA - The path to the directory for the data for a given unit test suite.

  Expected value: tests/unit/libstore/data/libstore or similar

Used by Lix

• _NIX_FORCE_HTTP - Forces file URIs to be treated as remote ones.

  Used by src/libfetchers/git.cc, src/libstore/http-binary-cache-store.cc, src/libstore/local-binary-cache-store.cc. Seems to be for forcing Git clones of git+file:// URLs, making the HTTP binary cache store accept file:// URLs (presumably passing them to curl?), and unknown reasons for the local binary cache.

  FIXME(jade): is this obscuring a bug in https://git.lix.systems/lix-project/lix/issues/200?

  Expected value: 1

• NIX_ATTRS_SH_FILE, NIX_ATTRS_JSON_FILE (output) - Set by Lix builders; see structuredAttrs documentation.

• NIX_BIN_DIR, NIX_STORE_DIR (or its inconsistently-used old alias NIX_STORE), NIX_DATA_DIR, NIX_LOG_DIR, NIX_LOG_DIR, NIX_STATE_DIR, NIX_CONF_DIR - Overrides compile-time configuration of various locations used by Lix. See src/libstore/globals.cc.

  Expected value: a directory

• NIX_DAEMON_SOCKET_PATH (optional) - Overrides the daemon socket path from $NIX_STATE_DIR/daemon-socket/socket.

  Expected value: path to a socket

• NIX_LOG_FD (output) - An FD number for logs in internal-json format to be sent to. Used for, mostly, "setPhase" in nixpkgs setup.sh, but can also be creatively used to print verbose log messages from derivations.

  Provided value: number corresponding to an FD in the builder

• NIX_PATH - Search path for <whatever>. Documented elsewhere in the manual.

  Expected value: : separated list of things that are not necessarily pointing to filesystem paths

• NIX_REMOTE - The default value of the Lix setting store.

  Expected value: "daemon", usually. Could be "auto" or any other value acceptable in store.

• NIX_BUILD_SHELL - Documented elsewhere; the shell to invoke with nix-shell but not nix develop/nix shell. The latter ignoring it altogether seems like a bug.

  Expected value: the path to an executable shell

• PRINT_PATH - Undocumented. Used by nix-prefetch-url as an alternative form of --print-path. Why???

• _NIX_IN_TEST - If present with any value, makes fetchClosure accept file URLs in addition to HTTP ones. Why is this not _NIX_FORCE_HTTP??

  Not used anywhere else.

• NIX_ALLOW_EVAL - Used by eval-cache tests to block evaluation if set to 0.

  Expected value: 1 or 0

• EDITOR - Used by editorFor(), which has some extremely sketchy editor-detection code for jumping to line numbers.

• LISTEN_FDS and LISTEN_PID - Used for systemd socket activation using the systemd socket activation protocol.

• NIX_PAGER (alternatively, PAGER) - Used to select a pager for Lix output. Why does this not use libutil getEnv()?

• LESS (output) - Sets the pager settings for less when invoked by Lix.

• NIX_IGNORE_SYMLINK_STORE - When set, Lix allows the store to be a symlink. Why do we support this?

  Apparently someone was using it enough to fix it.

• NIX_SSL_CERT_FILE (alternatively, SSL_CERT_FILE) - Used to set CA certificates for libcurl.

  Expected value: "/etc/ssl/certs/ca-certificates.crt" or similar

• NIX_REMOTE_SYSTEMS - Used to set builders. Can we please deprecate this?

• NIX_USER_CONF_FILES - : separated list of config files to load before /nix/nix.conf under each of XDG_CONFIG_DIRS.

• NIX_CONFIG - Newline separated configuration to load into Lix.

• NIX_GET_COMPLETIONS - Returns completions. Unsure of the exact format, someone should document it; either way my shell never had any completions.

  Expected value: number of completions to return.

• IN_SYSTEMD - Used to switch the logging format so that systemd gets the correct log levels. I think.

• NIX_HELD_LOCKS - Not used, what is this for?? We should surely remove it right after searching github?

• GC_INITIAL_HEAP_SIZE - Used to set the initial heap size, processed by boehmgc.

• NIX_COUNT_CALLS - Documented elsewhere; prints call counts for profiling purposes.

• NIX_SHOW_STATS - Documented elsewhere; prints various evaluation statistics like function calls, gc info, and similar.

• NIX_SHOW_STATS_PATH - Writes those statistics into a file at the given path instead of stdout. Undocumented.

• NIX_SHOW_SYMBOLS - Dumps the symbol table into the show-stats json output.

• TERM - If dumb or unset, disables ANSI colour output.

• NO_COLOR, NOCOLOR - Disables ANSI colour output.

• _NIX_DEVELOPER_SHOW_UNKNOWN_LOCATIONS - Highlights unknown locations in errors.

• NIX_PROFILE - Selects which profile nix-env will operate on. Documented elsewhere.

• NIX_SSHOPTS - Options passed to ssh(1) when using a ssh remote store. Incorrectly documented on nix-copy-closure which is surely not the only place they are used??

• _NIX_TEST_NO_LSOF - Used on non-Linux, non-macOS platforms to disable using lsof when finding gc roots.

  Since https://git.lix.systems/lix-project/lix/issues/156 was fixed, this should probably just be removed as it was a bad workaround for a macOS issue.

• _NIX_TEST_GC_SYNC_1 - Path to a pipe that is used to block the GC briefly to validate invariants from the test suite.

• _NIX_TEST_GC_SYNC_2 - Path to a pipe that is used to block the GC briefly to validate invariants from the test suite.

• _NIX_TEST_FREE_SPACE_FILE - Path to a file containing a decimal number with the free space that the GC is to believe it has.

• Various XDG vars

• NIX_DEBUG_SQLITE_TRACES - Dump all sqlite queries to the log at notice level.

• _NIX_TEST_NO_SANDBOX - Disables actually setting up the sandbox on macOS while leaving other logic the same. Unused on other platforms.

• _NIX_TRACE_BUILT_OUTPUTS - Dumps all the derivation paths alongside their outputs as lines into a file of the given name.

Used by the functional test framework

• NIX_DAEMON_PACKAGE - Runs the test suite against an alternate Nix daemon with the current client.

  Expected value: something like /nix/store/...-nix-2.18.2

• NIX_CLIENT_PACKAGE - Runs the test suite against an alternate Nix client with the current daemon.

  Expected value: something like /nix/store/...-nix-2.18.2

• NIX_TESTS_CA_BY_DEFAULT - Pass __contentAddressed, outputHashMode and outputHashAlgo to builds of some input-addressed derivations in the test suite.

  Expected value: 1

• TEST_DATA - Not an environment variable! This is used in repl characterization tests to refer to tests/functional/repl_characterization/data. More specifically, that path is replaced with the string $TEST_DATA in output for reproducibility.

• TEST_HOME (output) - Set to the temporary directory that is set as $HOME inside the tests, underneath $TEST_ROOT.

• TEST_ROOT (output) - Set to the temporary directory that is created for each test to mess with.

• _NIX_TEST_DAEMON_PID (output) - Used to track the daemon pid to be able to kill it.

  Provided value: Daemon pid as a base-10 integer, e.g. 2345