Fixing test failures

Author: lucasimi

src/tdamapper/_common.py

@@ -26,12 +26,12 @@ def _is_sparse(self, X):
         return hasattr(X, 'toarray')
 
     def _validate_X_y(self, X, y):
-        X = np.asarray(X)
-        y = np.asarray(y)
-
         if self._is_sparse(X):
             raise ValueError('Sparse data not supported.')
 
+        X = np.asarray(X)
+        y = np.asarray(y)
+
         if X.size == 0:
             msg = f'0 feature(s) (shape={X.shape}) while a minimum of 1 is required.'
             raise ValueError(msg)