Add test instructions

README.md

@@ -93,6 +93,39 @@ Only checkpoints for `Lagrange` or `DG` functions are supported from legacy DOLF
 
 See the [API](./docs/api) for more information.
 
+## Testing
+
+This library uses `pytest` for testing.
+To execute the tests, one should first install the library and its dependencies, as listed above.
+Then, can execute all tests by calling 
+```bash
+python3 -m pytest .
+```
+
+### Testing against data from legacy dolfin
+Some tests check the capability of reading data created with the legacy version of DOLFIN.
+To create this dataset, start a docker container with legacy DOLFIN, for instance: 
+```bash
+docker run -ti -v $(pwd):/root/shared -w /root/s
+hared --rm ghcr.io/scientificcomputing/fenics:2024-02-19
+```
+Then, inside this container, call
+```bash
+python3 ./tests/create_legacy_data.py --output-dir=legacy
+```
+
+### Testing against data from older versions of ADIOS4DOLFINx
+Some tests check the capability to read data generated by `adios4dolfinx<0.7.2`.
+To generate data for these tests use the following commands:
+```bash
+docker run -ti -v $(pwd):/root/shared -w /root/shared --rm ghcr.io/fenics/dolfinx/dolfinx:v0.7.3
+```
+Then, inside the container, call
+```bash
+python3 -m pip install adios4dolfinx==0.7.1
+python3 ./tests/create_legacy_checkpoint.py --output-dir=legacy_checkpoint
+```
+
 ## Long term plan
 
 The long term plan is to get this library merged into DOLFINx (rewritten in C++ with appropriate Python-bindings).