Revert "Only test sparse when it can actually be imported."

This reverts commit 44681b6.

Author: hameerabbasi

tests/_helpers.py

@@ -14,9 +14,7 @@
     all_libraries.append('sparse')
 
 def import_(library, wrapper=False):
-    # CuPy requires a GPU
-    # `sparse` has a dependency conflict with NumPy 1.21
-    if library in {'cupy', 'sparse'}:
+    if library == 'cupy':
         pytest.importorskip(library)
     if wrapper:
         if 'jax' in library: