Issue #14: Test case added, imports corrected

Test case added to check  function with empty data.

sksurgerycore/algorithms/errors.py

@@ -3,7 +3,7 @@
 """Functions for point based registration using Orthogonal Procrustes."""
 
 import numpy as np
-from sksurgerycore.algorithms.procrustes import validate_procrustes_inputs
+import sksurgerycore.algorithms.procrustes as p
 
 
 def compute_fre(fixed, moving, rotation, translation):
@@ -19,7 +19,7 @@ def compute_fre(fixed, moving, rotation, translation):
     """
     # pylint: disable=assignment-from-no-return
 
-    validate_procrustes_inputs(fixed, moving)
+    p.validate_procrustes_inputs(fixed, moving)
 
     transformed_moving = np.matmul(rotation, moving.transpose()) + translation
     squared_error_elementwise = np.square(fixed

sksurgerycore/algorithms/procrustes.py

@@ -3,7 +3,7 @@
 """Functions for point based registration using Orthogonal Procrustes."""
 
 import numpy as np
-from sksurgerycore.algorithms.errors import compute_fre
+import sksurgerycore.algorithms.errors as e
 
 
 def validate_procrustes_inputs(fixed, moving):
@@ -116,6 +116,6 @@ def orthogonal_procrustes(fixed, moving):
     T[0][0] = tmp[0]
     T[1][0] = tmp[1]
     T[2][0] = tmp[2]
-    fre = compute_fre(fixed, moving, R, T)
+    fre = e.compute_fre(fixed, moving, R, T)
 
     return R, T, fre

tests/algorithms/test_errors.py

@@ -3,6 +3,12 @@
 import six
 import numpy as np
 import pytest
-import sksurgerycore.algorithms.procrustes as p
+import sksurgerycore.algorithms.errors as e
+
+
+def test_empty_fixed():
+
+    with pytest.raises(TypeError):
+        e.compute_fre(None, None, np.ones(1, 3), np.ones(3, 3))