Testing - Lix Reference Manual

# 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

>     …
>     ├── lix
>     │   ├── 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 `lix/${library_shortname}/tests` within the directory for the library (`lix/${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 `lix/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.

### Inspecting failures

The test suite emits logs in `build/meson-logs/`; the full textual failure logs are in `build/meson-logs/testlog.txt`.

If you want a much nicer experience of viewing the logs in a structured manner, use `xunit-viewer --results build/meson-logs/testlog.junit.xml --server` to view them in a web browser.

### 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

FIXME(meson): this section is wrong for meson and commented out accordingly. See "Running Tests" above, and ask the Lix team if you need further clarification.

### 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

FIXME(meson): the command here is incorrect for meson and this whole functionality may need rebuilding.

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.

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

Installer tests section is outdated and commented out, see https://git.lix.systems/lix-project/lix/issues/33

## 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 `lix/` 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 `lix/libfetchers/git.cc`, `lix/libstore/http-binary-cache-store.cc`, `lix/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 `lix/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.

- `FORCE_COLOR`, `CLICOLOR_FORCE` - Enables ANSI colour output if `NO_COLOR`/`NOCOLOR` not set.

- `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_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`

- `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