[Fix] Also reject negative pos values

pyerrors/covobs.py

@@ -31,8 +31,8 @@ class Covobs:
                 else:
                     raise ValueError('Have to specify position of cov-element belonging to mean!')
             else:
-                if pos >= self.N:
+                if pos < 0 or pos >= self.N:
-                    raise ValueError(f'pos {pos} too large for covariance matrix with dimension {self.N}x{self.N}!')
+                    raise ValueError(f'pos {pos} not valid for covariance matrix with dimension {self.N}x{self.N}!')
             self._grad = np.zeros((self.N, 1))
             self._grad[pos] = 1.
         else:

tests/covobs_test.py

@@ -115,3 +115,9 @@ def test_covobs_pos_too_large():
     cov = [[1, 0], [0, 1]]
     with pytest.raises(ValueError):
         Covobs(1.0, cov, 'test', pos=2)
+
+
+def test_covobs_pos_negative():
+    cov = [[1, 0], [0, 1]]
+    with pytest.raises(ValueError):
+        Covobs(1.0, cov, 'test', pos=-1)