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).

## Specifying a subset of tests to run

You can use the tag query interface to specify the exact tests you want to run.
For instance, if you want to run only with `gem5.opt`, you can use

```shell
./main.py run --variant opt
```

Or, if you want to just run quick tests with the `gem5.opt` binary:

```shell
./main.py run --length quick --variant opt
```


To view all of the available tags, use

```shell
./main.py list --all-tags
```

The output is split into tag *types* (e.g., isa, variant, length) and the
tags for each type are listed after the type name.

Note that when using the isa tag type, tests were traditionally sorted based
on what compilation it required. However, as tests have switched to all be
compiled under the ALL compilation, which includes all ISAs so one doesn't
need to compile each one individually, using the isa tag for ISAs other than
ALL has become a less optimal way of searching for tests.  It would instead
be better to run subsets of tests based on their directories, as described
above.

You can specify "or" between tags within the same type by using the tag flag
multiple times. For instance, to run everything that is tagged "opt" or "fast"
use

```shell
./main.py run --variant opt --variant fast
```

You can also specify "and" between different types of tags by specifying more
than one type on the command line. For instance, this will only run tests with
both the "ALL" and "opt" tags.

```shell
./main.py run --isa All --variant opt
```

## 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).


## Binary test applications

The code for some test binaries that are run in the gem5 guest during
testing can be found in `tests/test-progs`.
There's one directory per test application.
The source code is under the `source` directory.

You may have a `bin` directory as well.
The `bin` directory is automatically created when running the test case that
uses the test binary.
This is not the case when a test is run via the --bin-path option.
In that scenario a bin directory will be created in the selected path
rather than in `tests/test-progs`.
The binary is downloaded from the gem5 servers the first
time it is referenced by a test.

Some other tests (like Linux-boot) don't have sources inside gem5 and
are simply downloaded from gem5 servers.

## Updating the test binaries

The test infrastructure should check with the gem5 servers to ensure you have
the latest binaries. However, if you believe your binaries are out of date,
simply delete the `bin` directory and they will be re-downloaded to your local
machine.

## Building (new-style) test binaries

In each `src/` directory under `tests/test-progs`, there is a Makefile.
This Makefile downloads a docker image and builds the test binary for some ISA
(e.g., Makefile.x86 builds the binary for x86). Additionally, if you run `make
upload` it will upload the binaries to the gem5 server, if you have access to
modify the binaries. *If you need to modify the binaries for updating a test or
adding a new test and you don't have access to the gem5 server, contact a
maintainer (see MAINTAINERS).*


## 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

## 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.