[tests] simplify demo test by using pytest-regressions

Author: renefritze

.ci/requirements-ci.txt

@@ -2,4 +2,5 @@ pytest
 wheel
 build
 pytest
-pytest-regressions
+pytest-regressions
+pandas

README.md

@@ -21,3 +21,9 @@ Development notes
 We have a `pre-commit` config that is also run/checked in CI.
 Python source is formatted with `black`.
 C++ source is formatted with `clang-format`.
+
+Dependencies for running the test suite can be installed with
+
+```
+python -m pip install -r ./.ci/requirements-ci.txt
+```

test/demo_result.pickle

@@ -1,20 +1,7 @@
-import pickle
-from pathlib import Path
-import numpy as np
-
-
-def test_demo_results():
-    fn = Path(__file__).resolve().parent / "demo_result.pickle"
-    good_result = pickle.load(open(str(fn), "rb"))
-
+def test_demo_results(ndarrays_regression):
     from pymor_dealii.pymor.demo import run
 
     result, _, _, _ = run(plot_error=False)
-    pickle.dump(
-        result,
-        open(Path(__file__).resolve().parent / "actual_demo_result.pickle", "wb"),
-    )
 
     compare = ["errors", "basis_sizes", "rel_errors"]
-    for key in compare:
-        assert np.allclose(result[key], good_result[key])
+    ndarrays_regression.check({k: v for k, v in result.items() if k in compare})