style: Fix flake8 violations in test_interpolation.py

- Add blank lines before nested class methods (E306)
- Split long lines to comply with 90 character limit (E501)

Author: ggorman

tests/test_interpolation.py

@@ -1190,18 +1190,21 @@ def test_interpolate_multiple_subdomains_unique_temps(self, mode):
         # Create 3 non-overlapping subdomains
         class LeftDomain(SubDomain):
             name = 'left'
+
             def define(self, dimensions):
                 x, y = dimensions
                 return {x: ('left', 3), y: y}
 
         class MiddleDomain(SubDomain):
             name = 'middle'
+
             def define(self, dimensions):
                 x, y = dimensions
                 return {x: ('middle', 3, 3), y: y}
 
         class RightDomain(SubDomain):
             name = 'right'
+
             def define(self, dimensions):
                 x, y = dimensions
                 return {x: ('right', 3), y: y}
@@ -1229,9 +1232,12 @@ def define(self, dimensions):
         sr_right = SparseFunction(name='sr_right', grid=grid, npoint=2)
 
         # Points: one inside each subdomain, one outside
-        sr_left.coordinates.data[:] = np.array([[1.5, 5.0], [8.5, 5.0]])    # Inside left, outside
-        sr_middle.coordinates.data[:] = np.array([[5.5, 5.0], [1.5, 5.0]])  # Inside middle, outside
-        sr_right.coordinates.data[:] = np.array([[9.5, 5.0], [5.5, 5.0]])   # Inside right, outside
+        # Inside left, outside
+        sr_left.coordinates.data[:] = np.array([[1.5, 5.0], [8.5, 5.0]])
+        # Inside middle, outside
+        sr_middle.coordinates.data[:] = np.array([[5.5, 5.0], [1.5, 5.0]])
+        # Inside right, outside
+        sr_right.coordinates.data[:] = np.array([[9.5, 5.0], [5.5, 5.0]])
 
         # Create operator with all 3 interpolations
         rec_left = sr_left.interpolate(f_left)
@@ -1260,9 +1266,11 @@ def define(self, dimensions):
                 f"Rank {rank}: Suspicious large value in {sr.name}.data: {sr.data}"
 
     @pytest.mark.parallel(mode=4)
-    @pytest.mark.skip(reason="Test has degenerate MPI decomposition causing intermittent failures. "
-                             "Use test_interpolate_subdomain_mpi_mfe or "
-                             "test_interpolate_multiple_subdomains_unique_temps instead.")
+    @pytest.mark.skip(reason="Test has degenerate MPI decomposition causing "
+                             "intermittent failures. Use "
+                             "test_interpolate_subdomain_mpi_mfe or "
+                             "test_interpolate_multiple_subdomains_unique_temps "
+                             "instead.")
     def test_interpolate_subdomain_mpi(self, mode):
         """
         Test interpolation off of a Function defined on a SubDomain with MPI.