Testing your contributions
Each feature added to clan should be tested extensively via automated tests.
This document covers different methods of automated testing, including creating, running and debugging such tests.
In order to test the behavior of clan, different testing frameworks are used depending on the concern:
- NixOS VM tests: for high level integration
- NixOS container tests: for high level integration
- Python tests via pytest: for unit tests and integration tests
- Nix eval tests: for nix functions, libraries, modules, etc.
NixOS VM Tests
The NixOS VM Testing Framework is used to create high level integration tests, by running one or more VMs generated from a specified config. Commands can be executed on the booted machine(s) to verify a deployment of a service works as expected. All machines within a test are connected by a virtual network. Internet access is not available.
When to use VM tests
- testing that a service defined through a clan module works as expected after deployment
- testing clan-cli subcommands which require accessing a remote machine
When not to use VM tests
NixOS VM Tests are slow and expensive. They should only be used for testing high level integration of components. VM tests should be avoided wherever it is possible to implement a cheaper unit test instead.
- testing detailed behavior of a certain clan-cli command -> use unit testing via pytest instead
- regression testing -> add a unit test
Finding examples for VM tests
Existing nixos vm tests in clan-core can be found by using ripgrep:
Locating definitions of failing VM tests
All nixos vm tests in clan are exported as individual flake outputs under checks.x86_64-linux.{test-attr-name}
.
If a test fails in CI:
- look for the job name of the test near the top if the CI Job page, like, for example
gitea:clan/clan-core#checks.x86_64-linux.borgbackup/1242
- in this case
checks.x86_64-linux.borgbackup
is the attribute path - note the last element of that attribute path, in this case
borgbackup
- search for the attribute name inside the
/checks
directory via ripgrep
example: locating the vm test named borgbackup
:
$ rg "borgbackup =" ./checks
./checks/flake-module.nix
41: borgbackup = import ./borgbackup nixosTestArgs;
-> the location of that test is /checks/flake-module.nix
line 41
.
Adding vm tests
Create a nixos test module under /checks/{name}/default.nix
and import it in /checks/flake-module.nix
.
Running VM tests
(replace{test-attr-name}
with the name of the test)
Debugging VM tests
The following techniques can be used to debug a VM test:
Print Statements
Locate the definition (see above) and add print statements, like, for example print(client.succeed("systemctl --failed"))
, then re-run the test via nix build
(see above)
Interactive Shell
- Execute the vm test outside the nix Sandbox via the following command:
nix run .#checks.x86_64-linux.{test-attr-name}.driver -- --interactive
- Then run the commands in the machines manually, like for example:
Breakpoints
To get an interactive shell at a specific line in the VM test script, add a breakpoint()
call before the line to debug, then run the test outside of the sandbox via:
nix run .#checks.x86_64-linux.{test-attr-name}.driver
NixOS Container Tests
Those are very similar to NixOS VM tests, as in they run virtualized nixos machines, but instead of using VMs, they use containers which are much cheaper to launch. As of now the container test driver is a downstream development in clan-core. Basically everything stated under the NixOS VM tests sections applies here, except some limitations.
Limitations:
- does not yet support networking
- supports only one machine as of now
Where to find examples for NixOS container tests
Existing nixos container tests in clan-core can be found by using ripgrep:
Python tests via pytest
Since the clan cli is written in python, the pytest
framework is used to define unit tests and integration tests via python
Due to superior efficiency,
When to use python tests
- writing unit tests for python functions and modules, or bugfixes of such
- all integrations tests that do not require building or running a nixos machine
- impure integrations tests that require internet access (very rare, try to avoid)
When not to use python tests
- integrations tests that require building or running a nixos machine (use NixOS VM or container tests instead)
- testing behavior of a nix function or library (use nix eval tests instead)
Finding examples of python tests
Existing python tests in clan-core can be found by using ripgrep:
Locating definitions of failing python tests
If any python test fails in the CI pipeline, an error message like this can be found at the end of the log:
...
FAILED tests/test_machines_cli.py::test_machine_delete - clan_cli.errors.ClanError: Template 'new-machine' not in 'inputs.clan-core
...
In this case the test is defined in the file /tests/test_machines_cli.py
via the test function test_machine_delete
.
Adding python tests
If a specific python module is tested, the test should be located near the tested module in a subdirectory called ./tests
If the test is not clearly related to a specific module, put it in the top-level ./tests
directory of the tested python package. For clan-cli
this would be /pkgs/clan-cli/clan_cli/tests
.
All filenames must be prefixed with test_
and test functions prefixed with test_
for pytest to discover them.
Running python tests
Running all python tests
To run all python tests which are executed in the CI pipeline locally, use this nix build
command
Running a specific python test
To run a specific python test outside the nix sandbox
- Enter the development environment of the python package, by either:
- Having direnv enabled and entering the directory of the package (eg.
/pkgs/clan-cli
) - Or using the command
select-shell {package}
in the top-level dev shell of clan-core, (eg.switch-shell clan-cli
) - Execute the test via pytest using issuing
pytest ./path/to/test_file.py:test_function_name -s -n0
The flags -sn0
are useful to forwards all stdout/stderr output to the terminal and be able to debug interactively via breakpoint()
.
Debugging python tests
To debug a specific python test, find its definition (see above) and make sure to enter the correct dev environment for that python package.
Modify the test and add breakpoint()
statements to it.
Execute the test using the flags -sn0
in order to get an interactive shell at the breakpoint:
Nix Eval Tests
When to use nix eval tests
Nix eval tests are good for testing any nix logic, including
- nix functions
- nix libraries
- modules for the nixos module system
When not to use
- tests that require building nix derivations (except some very cheap ones)
- tests that require running programs written in other languages
- tests that require building or running nixos machines
Finding examples of nix eval tests
Existing nix eval tests can be found via this ripgrep command:
Locating definitions of failing nix eval tests
Failing nix eval tests look like this:
> ✅ test_attrsOf_attrsOf_submodule
> ✅ test_attrsOf_submodule
> ❌ test_default
> /build/nix-8-2/expected.nix --- Nix
> 1 { foo = { bar = { __prio = 1500; }; } 1 { foo = { bar = { __prio = 1501; }; }
> . ; } . ; }
>
>
> ✅ test_no_default
> ✅ test_submodule
> ✅ test_submoduleWith
> ✅ test_submodule_with_merging
>
> 😢 6/7 successful
> error: Tests failed
To locate the definition, find the flake attribute name of the failing test near the top of the CI Job page, like for example gitea:clan/clan-core#checks.x86_64-linux.lib-values-eval/1242
.
In this case lib-values-eval
is the attribute we are looking for.
Find the attribute via ripgrep:
$ rg "lib-values-eval ="
lib/values/flake-module.nix
21: lib-values-eval = pkgs.runCommand "tests" { nativeBuildInputs = [ pkgs.nix-unit ]; } ''
grmpf@grmpf-nix ~/p/c/clan-core (test-docs)>
In this case the test is defined in the file lib/values/flake-module.nix
line 21
Adding nix eval tests
In clan core, the following pattern is usually followed:
- tests are put in a
test.nix
file - a CI Job is exposed via a
flake-module.nix
- that
flake-module.nix
is imported via theflake.nix
at the root of the project
For example see /lib/values/{test.nix,flake-module.nix}
.
Running nix eval tests
Since all nix eval tests are exposed via the flake outputs, they can be ran via nix build
:
For quicker iteration times, instead of nix build
use the nix-unit
command available in the dev environment.
Example:
Debugging nix eval tests
Follow the instructions above to find the definition of the test, then use one of the following techniques:
Print debugging
Add lib.trace
or lib.traceVal
statements in order to print some variables during evaluation
Nix repl
Use nix repl
to evaluate to inspec the test.
Each test consists opf an expr
(expression) and an expected
field. nix-unit
simply checks if expr == expected
and prints the diff if that's not the case.
nix repl
can be used to inspect expr
manually, or any other variables that you choose to expose.
Example:
$ nix repl
Nix 2.25.5
Type :? for help.
nix-repl> tests = import ./lib/values/test.nix {}
nix-repl> tests
{
test_attrsOf_attrsOf_submodule = { ... };
test_attrsOf_submodule = { ... };
test_default = { ... };
test_no_default = { ... };
test_submodule = { ... };
test_submoduleWith = { ... };
test_submodule_with_merging = { ... };
}
nix-repl> tests.test_default.expr
{
foo = { ... };
}