gem5/TESTING.md

This file explains how to use gem5's updated testing infrastructure. Running
tests before submitting a patch is *incredibly important* so unexpected bugs
don't creep into gem5.

gem5's testing infrastructure has the following goals:
 * Simple for *all* users to run
 * Fast execution in the simple case
 * High coverage of gem5 code

## Running unit tests

gem5 comes with unit tests, created using the Google Test framework. These can
be built through SCons.

To build and run all the unit tests:

```shell
scons build/ALL/unittests.opt
```

All unit tests should be run prior to creating a pull request at
https://github.com/gem5/gem5/pulls/

To compile and run just one set of tests (e.g. those declared within
`src/base/bitunion.test.cc`):

```shell
scons build/ALL/base/bitunion.test.opt
./build/ALL/base/bitunion.test.opt
```

To list the available test functions from a test file:

```shell
./build/ALL/base/bitunion.test.opt --gtest_list_tests
```

To run a specific test function (e.g., BitUnionData.NormalBitfield):

```shell
./build/ALL/base/bitunion.test.opt --gtest_filter=BitUnionData.NormalBitfield
```

## Running system-level tests

Within the `tests` directory we have system-level tests. These tests run
the gem5 framework against various hardware configurations, with different
ISAs, then verify the simulations execute correctly. These should be seen as
high-level, coarse-grained tests to compliment the unit-tests.

Below is the most common way the tests are run. This will run all of the
"quick" tests for X86, ARM, and RISC-V. These tests make up our best-supported
platforms and use cases. When running these tests, you will likely want to us
the option `-j <CPUs>` where `CPUs` is as large as you can make it.
Additionally, it is often a good idea to run longer tests (e.g., linux boot)
before submitting your patch.

```shell
cd tests
./main.py run
```

The above is the *minumum* you should run before posting a pull request to
https://github.com/gem5/gem5/pulls/

## Running tests from multiple directories

The command line above will walk the directory tree starting from the cwd
(tests), and it will run every test it encounters in its path. It is possible
to specify multiple root directories by providing several positional
arguments:

```shell
./main.py run <directory1> <directory2> [...]
```

This will load every test in directory1 and directory2 (and their
subdirectories).

### 'quick', 'long', and 'very-long' tests

There are three categoties of tests which may be run from the "tests" directory:

1. **'quick' tests**. This suite of tests are designed to finish execution in a few hours, inclusive of compilation of gem5.
We run these as part of our continuous integration tests on pull requests made to our repository.
These tests all utilize a binary build `scons build/ALL/gem5.opt`, and thus only rely on a single compilation for the tests to run.
2. **'long' tests**. This suite of tests are designed to finish execution in around 12 hours.
They incorporate longer running tests which are unsuitable to run as part of the 'quick' tests.
We run these daily via a scheduled job.
3. **'very-long' tests**. This suite of tests are designed to finish execution in days.
They incorporate tests which are too long to run frequntly
We run these daily via a scheduled job.

When executing `./main.py run` the 'quick' tests are executed.
To run the 'long' tests execute:

```sh
./main.py run --length=long
```

and to run the 'very-long' tests execute:

```sh
./main.py run --length=very-long
```

In most cases we recommend running the 'quick' tests for most changes.
Only in some cases, such as contributions which significantly change the codebase, do we recommend running the 'long' or 'very-long' suite.

### Running tests in batch

The testing infrastructure provides the two needed methods to run tests in
batch. First, you can list all of the tests based on the same tags as above in
a machine-readable format by passing the `-q` flag. This will list all of the
*suites* that match the given tag(s).

```shell
./main.py list -q --suites
SuiteUID:tests/gem5/hello_se/test_hello_se.py:testhello64-static-X86-opt
SuiteUID:tests/gem5/hello_se/test_hello_se.py:testhello64-dynamic-X86-opt
SuiteUID:tests/gem5/hello_se/test_hello_se.py:testhello32-static-X86-opt
SuiteUID:tests/gem5/hello_se/test_hello_se.py:testhello64-static-ARM-opt
SuiteUID:tests/gem5/hello_se/test_hello_se.py:testhello32-static-ARM-opt
SuiteUID:tests/gem5/m5_util/test_exit.py:m5_exit_test-X86-opt
SuiteUID:tests/gem5/test_build/test_build.py:build-X86-opt
SuiteUID:tests/gem5/test_build/test_build.py:build-RISCV-opt
SuiteUID:tests/gem5/test_build/test_build.py:build-ARM-opt
```

Next, you can run a single *suite* from the command line by passing the option
`--uid`. For instance,

```shell
./main.py run --skip-build \
    --uid SuiteUID:tests/gem5/m5_util/test_exit.py:m5_exit_test-X86-opt
```

With this method, you can only run a *single* suite at a time. If you want to
run more than one uid, you must call `./main.py` multiple times.

Currently, you must specify `--skip-build` if you want to run a single suite or
run in batch mode. Otherwise, you will build gem5 for all architectures.

### Rerunning failed tests

While developing software a common practice is to run tests, make a change, and
assert that the tests still pass. If tests fail you'll likely want to
rerun and fix those specific tests without running redundant ones. The testing
infrastructure allows you to rerun tests which failed in the last execution by
using the `rerun` command.

```shell
./main.py run
#
#  Some tests fail...
#

# Rerun only the failed test suites (not the ones which passed).
./main.py rerun
```

### If something goes wrong

The first step is to turn up the verbosity of the output using `-v`. This will
allow you to see what tests are running and why a test is failing.

If a test fails, the temporary directory where the gem5 output was saved is kept
and the path to the directory is printed in the terminal.

### Debugging the testing infrastructure

Every command takes an option for the verbosity. `-v`, `-vv`, `-vvv` will
increase the verbosity level. If something isn't working correctly, you can
start here.

Most of the code for the testing infrastructure is in ext/testlib. This code
contains the base code for tests, suites, fixtures, etc. The code in tests/gem5
is *gem5-specific* code. For the most part, the code in tests/gem5 extends the
structures in ext/testlib.

### Common errors

You may see a number of lines of output during test discovery that look like
the following:

```shell
    Tried to load tests from ... but failed with an exception.
    Tried to load tests from ... but failed with an exception.
    ...
```

The testing library searches all python files in the `tests/` directory. The
test library executes each python file it finds searching for tests. It's okay
if the file causes an exception. This means there are no tests in that file
(e.g., it's not a new-style test).

### Running Tests in Parallel

Whimsy has support for parallel testing baked in. This system supports
running multiple suites at the same time on the same computer. To run
suites in parallel, supply the `-t <number-tests>` flag to the run command.

For example, to run up to three test suites at the same time::

    ./main.py run --skip-build -t 3

### Testing resources

By default binaries and testing resources are obtained via the [gem5 resources infrastructure](https://www.gem5.org/documentation/general_docs/gem5_resources/).
The downloaded resources are cached in "tests/gem5/resources".
The resources are cached to avoid re-downloading when tests are run multiple times, though some of these resources, such as disk images, are large.
It is therefore recommended you remove the "tests/gem5/resources" directory when you are done testing.

## Running Tests within GitHub Actions

To run these tests within GitHub Actions, we use the format of running
tests by directory as shown above in the "Running Tests from Multiple
Directories" section.  These tests are run within workflow files,
which can be found in the .github directory of this repository.
You can learn more about workflows
[here](https://docs.github.com/en/actions/using-workflows/about-workflows).

Each workflow is made up of individual jobs, where each job is a set
of tests that is executed on a runner within GitHub.  In each
workflow, each version of gem5.opt needed is first built, and then
stored as an artifact for main.py to use.

There are two sets of runners within the gem5 repository: builders and
runners.  The builders have more resources available to allow for a
quicker compilation of gem5, while the runners have less, and are
meant to only run tests.

After the gem5 artifact has been uploaded, a runner can then download
the versions needed for their tests.  For example, in the daily-tests.yaml,
in order to run the multi_isa tests, you need artifacts of ARM, RISCV,
and VEGA_X86.

## Adding Tests to GitHub Actions

In order to add new tests to our GitHub Actions testing infastructure,
follow the format currently shown in the existing workflows.  If the
new tests were added to an already existing directory (ex. A very-long
test in the gem5_library_example_tests), it will automatically be
included into the weekly testing, since weekly-tests.yaml already
contains a job for the gem5_library_example_tests.

However, if a new directory is added to the tests, you need to manually
add a new step to the GitHub workflows.  This would consist of both a
step to build whatever version of gem5 was required if it wasn't
already included in the file, as well as a step to run main.py
in the given directory after downloading the gem5 artifact.