# 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`, which includes unit tests from
subtrees, or `make && make -C src check-unit` for just the unit tests.

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 some of the command line arguments accepted by
`bitcoind`. Use `--` to separate these sets of arguments:

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

The `-printtoconsole=1` after the two dashes sends debug logging, which
normally goes only to `debug.log` within the data directory, also to the
standard terminal output.

... or to run just the doubledash test:

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

`test_bitcoin` creates a temporary working (data) directory with a randomly
generated pathname within `test_common_Bitcoin Core/`, which in turn is within
the system's temporary directory (see
[`temp_directory_path`](https://en.cppreference.com/w/cpp/filesystem/temp_directory_path)).
This data directory looks like a simplified form of the standard `bitcoind` data
directory. Its content will vary depending on the test, but it will always
have a `debug.log` file, for example.

The location of the temporary data directory can be specified with the
`-testdatadir` option. This can make debugging easier. The directory
path used is the argument path appended with
`/test_common_Bitcoin Core/<test-name>/datadir`.
The directory path is created if necessary.
Specifying this argument also causes the data directory
not to be removed after the last test. This is useful for looking at
what the test wrote to `debug.log` after it completes, for example.
(The directory is removed at the start of the next test run,
so no leftover state is used.)

```bash
$ test_bitcoin --run_test=getarg_tests/doubledash -- -testdatadir=/somewhere/mydatadir
Test directory (will not be deleted): "/somewhere/mydatadir/test_common_Bitcoin Core/getarg_tests/doubledash/datadir
Running 1 test case...

*** No errors detected
$ ls -l '/somewhere/mydatadir/test_common_Bitcoin Core/getarg_tests/doubledash/datadir'
total 8
drwxrwxr-x 2 admin admin 4096 Nov 27 22:45 blocks
-rw-rw-r-- 1 admin admin 1003 Nov 27 22:45 debug.log
```

If you run an entire test suite, such as `--run_test=getarg_tests`, or all the test suites
(by not specifying `--run_test`), a separate directory
will be created for each individual test.

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

### 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
```