[Doc] Describe steps for running and debugging tests

doc/sphinx/develop/index.md

@@ -54,6 +54,7 @@ This section is a work in progress.
 - [](CONTRIBUTING)
 - [](style-guidelines)
 - [](writing-tests)
+- [](running-tests)
 - [](writing-examples)
 - [](doc-formatting)
 
@@ -64,6 +65,7 @@ This section is a work in progress.
 CONTRIBUTING
 style-guidelines
 writing-tests
+running-tests
 writing-examples
 doc-formatting
 ```

doc/sphinx/develop/running-tests.md

@@ -0,0 +1,154 @@
+# Running Tests and Debugging
+
+## Using Cantera from the Build Directory
+
+After compiling Cantera from source, it is convenient to use the Cantera Python module
+directly without fully installing Cantera. Doing this requires some special
+configuration to make sure your operating system and Python installation can find all
+the relevant files.
+
+### Temporary Configuration
+
+To use the Python module from the build directory for the duration of the current
+shell session, run the following commands from the root of the Cantera source directory:
+
+::::{tab-set}
+:::{tab-item} Linux
+:sync: linux
+```sh
+export LD_LIBRARY_PATH=$(pwd)/build/lib
+export PYTHONPATH=$(pwd)/build/python
+```
+:::
+
+:::{tab-item} macOS
+:sync: macos
+```sh
+export DYLD_LIBRARY_PATH=$(pwd)/build/lib
+export PYTHONPATH=$(pwd)/build/python
+```
+:::
+
+:::{tab-item} Windows (PowerShell)
+:sync: windows
+```pwsh
+$Env:PYTHONPATH = (Get-Location).Path + '\build\python'
+```
+:::
+::::
+
+After this, you will be able to use the Cantera Python module from the terminal where
+these commands were executed. For example:
+
+```sh
+# start an interactive shell and then import Cantera
+ipython
+
+# convert a mechanism
+python -m cantera.ck2yaml --inp=...
+
+# run an example
+python samples/python/onedim/adiabatic_flame.py
+```
+
+### Permanent Configuration Using Conda
+
+The following commands will make the Cantera Python module in the build directory
+available within the current Conda environment.
+
+::::{tab-set}
+:::{tab-item} Linux
+:sync: linux
+```sh
+conda env config vars set LD_LIBRARY_PATH=$(pwd)/build/lib
+conda env config vars set PYTHONPATH=$(pwd)/build/python
+
+```
+:::
+
+:::{tab-item} macOS
+:sync: macos
+```sh
+conda env config vars set DYLD_LIBRARY_PATH=$(pwd)/build/lib
+conda env config vars set PYTHONPATH=$(pwd)/build/python
+```
+:::
+
+:::{tab-item} Windows (PowerShell)
+:sync: windows
+```pwsh
+New-Item -Type Junction -Target ((Get-Location).Path + '\build\python\cantera') -Path ($Env:CONDA_PREFIX + '\lib\site-packages\cantera')
+```
+:::
+::::
+
+Setting up the paths this way can be useful if you're using an IDE such as VS Code that
+is aware of Conda environments and may allow you to run tests within the IDE.
+
+## Running Individual Python Tests and Test Subsets
+
+To run the full Python test suite:
+
+```sh
+pytest -raP --verbose test/python
+```
+
+To run tests from a specific file:
+```sh
+pytest -raP --verbose test/python/test_composite.py
+```
+
+To run tests where the name matches a specific pattern:
+```sh
+pytest -raP --verbose test/python -k 'add_rxn'
+```
+
+To have the test runner activate a PDB shell after a failed assertion:
+```sh
+pytest -raP --verbose --pdb test/python```
+```
+
+```{important}
+Remember to run `scons build` after any code change before running tests directly with
+`pytest`.
+```
+
+## Running tests through GDB
+
+If you are trying to debug a problem that results in a segmentation fault (crash)
+during the test, you can try running it inside the debugger. The following notes may
+help with running either the C++ or Python tests through GDB on Linux.
+
+- Build the source code with debugging information enabled and optimizations disabled.
+  It can also help to enable certain bounds checks available in the standard library:
+  ```sh
+  scons build optimize=n debug=y debug_flags='-g -D_GLIBCXX_ASSERTIONS'
+  ```
+
+### Running C++ (GoogleTest) Tests
+
+First, run the target test through SCons to make sure the Cantera library and the test
+executable are up to date. We'll use the `kinetics` test subset as an example, with the
+goal of debugging the `PlogLowPressure` test.
+```sh
+scons test-kinetics
+```
+
+Next, we need to set some environment variables that specify where the test program
+can find files needed to run the tests. Normally, these are handled by SCons:
+```sh
+export CANTERA_DATA=test/data:data
+export PYTHONPATH=test/python:$PYTHONPATH
+```
+
+To start the debugger and enable only the desired test:
+```sh
+gdb --args build/test/kinetics/kinetics --gtest_filter="*PlogLowPressure"
+```
+
+Then at the `(gdb)` prompt, type `run` and press Enter.
+
+After the debugger reaches the error, the most useful command is the `where` command,
+which will print a stack trace. The `up` command will move up the stack each time it is
+called and print the corresponding line of the source code.
+