Merge branch 'develop' into documentation

pyerrors/obs.py

@@ -567,7 +567,8 @@ class Obs:
             for the given ensemble and replicum. The zeroth entry of the array contains
             the mean value of the Obs, entries 1 to N contain the N jackknife samples
             derived from the Obs. The current implementation only works for observables
-            defined on exactly one ensemble and replicum.
+            defined on exactly one ensemble and replicum. The derived jackknife samples
+            should agree with samples from a full jackknife analysis up to O(1/N).
         """
 
         if len(self.names) != 1:

tests/obs_test.py

@@ -519,3 +519,6 @@ def test_jackknife():
         tmp_jacks[i + 1] = (n * mean - full_data[i]) / (n - 1)
 
     assert np.allclose(tmp_jacks, my_obs.export_jackknife())
+    my_new_obs = my_obs + pe.Obs([full_data], ['test2'])
+    with pytest.raises(Exception):
+        my_new_obs.export_jackknife()