MAINT: test_linalg: use xp.stack not xp.asarray for nested arrays (#363)

Author: ev-br

Diff for: array_api_tests/test_linalg.py

@@ -206,11 +206,11 @@ def test_cross(x1_x2_kw):
 
     def exact_cross(a, b):
         assert a.shape == b.shape == (3,), "Invalid cross() stack shapes. This indicates a bug in the test suite."
-        return asarray([
+        return asarray(xp.stack([
             a[1]*b[2] - a[2]*b[1],
             a[2]*b[0] - a[0]*b[2],
             a[0]*b[1] - a[1]*b[0],
-        ], dtype=res.dtype)
+        ]), dtype=res.dtype)
 
     # We don't want to pass in **kw here because that would pass axis to
     # cross() on a single stack, but the axis is not meaningful on unstacked
@@ -267,7 +267,7 @@ def true_diag(x_stack, offset=0):
             x_stack_diag = [x_stack[i, i + offset] for i in range(diag_size)]
         else:
             x_stack_diag = [x_stack[i - offset, i] for i in range(diag_size)]
-        return asarray(x_stack_diag, dtype=x.dtype)
+        return asarray(xp.stack(x_stack_diag) if x_stack_diag else [], dtype=x.dtype)
 
     _test_stacks(linalg.diagonal, x, **kw, res=res, dims=1, true_val=true_diag)
 
@@ -901,7 +901,9 @@ def true_trace(x_stack, offset=0):
             x_stack_diag = [x_stack[i, i + offset] for i in range(diag_size)]
         else:
             x_stack_diag = [x_stack[i - offset, i] for i in range(diag_size)]
-        return _array_module.sum(asarray(x_stack_diag, dtype=x.dtype))
+        result = xp.asarray(xp.stack(x_stack_diag) if x_stack_diag else [], dtype=x.dtype)
+        return _array_module.sum(result)
+
 
     _test_stacks(linalg.trace, x, **kw, res=res, dims=0, true_val=true_trace)