Remove unused plt.show and ensure matplotlib figures are closed

Removed an unnecessary `plt.show()` call in the test to streamline the code. Added a `pytest_runtest_teardown` hook to automatically close all matplotlib figures after tests to prevent resource leaks and improve test isolation.

Author: LarsKue

tests/test_diagnostics/conftest.py

@@ -4,6 +4,12 @@
 from bayesflow.utils.numpy_utils import softmax
 
 
+def pytest_runtest_teardown(item, nextitem):
+    import matplotlib.pyplot as plt
+
+    plt.close("all")
+
+
 @pytest.fixture()
 def var_names():
     return [r"$\beta_0$", r"$\beta_1$", r"$\sigma$"]

tests/test_diagnostics/test_diagnostics_plots.py

@@ -46,10 +46,7 @@ def test_calibration_histogram(random_estimates, random_targets):
 
 
 def test_loss(history):
-    import matplotlib.pyplot as plt
-
     out = bf.diagnostics.loss(history)
-    plt.show()
     assert len(out.axes) == 1
     assert out.axes[0].title._text == "Loss Trajectory"