# Unit tests

The sources in this directory are unit test cases. Boost includes a
unit testing framework, and since Bitcoin Core already uses Boost, it makes
sense to simply use this framework rather than require developers to
configure some other framework (we want as few impediments to creating
unit tests as possible).

The build system is set up to compile an executable called `test_bitcoin`
that runs all of the unit tests. The main source file for the test library is found in
`util/setup_common.cpp`.

### Compiling/running unit tests

Unit tests will be automatically compiled if dependencies were met in `./configure`
and tests weren't explicitly disabled.

After configuring, they can be run with `make check`.

To run the unit tests manually, launch `src/test/test_bitcoin`. To recompile
after a test file was modified, run `make` and then run the test again. If you
modify a non-test file, use `make -C src/test` to recompile only what's needed
to run the unit tests.

To add more unit tests, add `BOOST_AUTO_TEST_CASE` functions to the existing
.cpp files in the `test/` directory or add new .cpp files that
implement new `BOOST_AUTO_TEST_SUITE` sections.

To run the GUI unit tests manually, launch `src/qt/test/test_bitcoin-qt`

To add more GUI unit tests, add them to the `src/qt/test/` directory and
the `src/qt/test/test_main.cpp` file.

### Running individual tests

`test_bitcoin` accepts the command line arguments from the boost framework.
For example, to run just the `getarg_tests` suite of tests:

```bash
test_bitcoin --log_level=all --run_test=getarg_tests
```

`log_level` controls the verbosity of the test framework, which logs when a
test case is entered, for example. `test_bitcoin` also accepts the command
line arguments accepted by `bitcoind`. Use `--` to separate both types of
arguments:

```bash
test_bitcoin --log_level=all --run_test=getarg_tests -- -printtoconsole=1
```

The `-printtoconsole=1` after the two dashes redirects the debug log, which
would normally go to a file in the test datadir
(`BasicTestingSetup::m_path_root`), to the standard terminal output.

... or to run just the doubledash test:

```bash
test_bitcoin --run_test=getarg_tests/doubledash
```

Run `test_bitcoin --help` for the full list.

### Adding test cases

To add a new unit test file to our test suite you need
to add the file to `src/Makefile.test.include`. The pattern is to create
one test file for each class or source file for which you want to create
unit tests. The file naming convention is `<source_filename>_tests.cpp`
and such files should wrap their tests in a test suite
called `<source_filename>_tests`. For an example of this pattern,
see `uint256_tests.cpp`.

### Logging and debugging in unit tests

`make check` will write to a log file `foo_tests.cpp.log` and display this file
on failure. For running individual tests verbosely, refer to the section
[above](#running-individual-tests).

To write to logs from unit tests you need to use specific message methods
provided by Boost. The simplest is `BOOST_TEST_MESSAGE`.

For debugging you can launch the `test_bitcoin` executable with `gdb` or `lldb` and
start debugging, just like you would with any other program:

```bash
gdb src/test/test_bitcoin
```

#### Segmentation faults

If you hit a segmentation fault during a test run, you can diagnose where the fault
is happening by running `gdb ./src/test/test_bitcoin` and then using the `bt` command
within gdb.

Another tool that can be used to resolve segmentation faults is
[valgrind](https://valgrind.org/).

If for whatever reason you want to produce a core dump file for this fault, you can do
that as well. By default, the boost test runner will intercept system errors and not
produce a core file. To bypass this, add `--catch_system_errors=no` to the
`test_bitcoin` arguments and ensure that your ulimits are set properly (e.g. `ulimit -c
unlimited`).

Running the tests and hitting a segmentation fault should now produce a file called `core`
(on Linux platforms, the file name will likely depend on the contents of
`/proc/sys/kernel/core_pattern`).

You can then explore the core dump using
```bash
gdb src/test/test_bitcoin core

(gbd) bt  # produce a backtrace for where a segfault occurred
```