Update test_cross to test broadcastable shapes

This also updates it to only test axes from [min(x1.ndim, x2.ndim), -1], as
per data-apis/array-api#740

array_api_tests/test_linalg.py

@@ -148,23 +148,29 @@ def cross_args(draw, dtype_objects=dh.real_dtypes):
     in the drawn axis.
 
     """
-    shape = list(draw(shapes()))
-    size = len(shape)
-    assume(size > 0)
+    shape1, shape2 = draw(two_mutually_broadcastable_shapes)
+    min_ndim = min(len(shape1), len(shape2))
+    assume(min_ndim > 0)
 
-    kw = draw(kwargs(axis=integers(-size, size-1)))
+    kw = draw(kwargs(axis=integers(-min_ndim, -1)))
     axis = kw.get('axis', -1)
-    shape[axis] = 3
-    shape = tuple(shape)
+    if draw(booleans()):
+        # Sometimes allow invalid inputs to test it errors
+        shape1 = list(shape1)
+        shape1[axis] = 3
+        shape1 = tuple(shape1)
+        shape2 = list(shape2)
+        shape2[axis] = 3
+        shape2 = tuple(shape2)
 
     mutual_dtypes = shared(mutually_promotable_dtypes(dtypes=dtype_objects))
     arrays1 = arrays(
         dtype=mutual_dtypes.map(lambda pair: pair[0]),
-        shape=shape,
+        shape=shape1,
     )
     arrays2 = arrays(
         dtype=mutual_dtypes.map(lambda pair: pair[1]),
-        shape=shape,
+        shape=shape2,
     )
     return draw(arrays1), draw(arrays2), kw
 
@@ -176,15 +182,17 @@ def test_cross(x1_x2_kw):
     x1, x2, kw = x1_x2_kw
 
     axis = kw.get('axis', -1)
-    err = "test_cross produced invalid input. This indicates a bug in the test suite."
-    assert x1.shape == x2.shape, err
-    shape = x1.shape
-    assert x1.shape[axis] == x2.shape[axis] == 3, err
+    if not (x1.shape[axis] == x2.shape[axis] == 3):
+        ph.raises(Exception, lambda: xp.cross(x1, x2, **kw),
+                  "cross did not raise an exception for invalid shapes")
+        return
 
     res = linalg.cross(x1, x2, **kw)
 
+    broadcasted_shape = sh.broadcast_shapes(x1.shape, x2.shape)
+
     assert res.dtype == dh.result_type(x1.dtype, x2.dtype), "cross() did not return the correct dtype"
-    assert res.shape == shape, "cross() did not return the correct shape"
+    assert res.shape == broadcasted_shape, "cross() did not return the correct shape"
 
     def exact_cross(a, b):
         assert a.shape == b.shape == (3,), "Invalid cross() stack shapes. This indicates a bug in the test suite."