Simplify test_can_cast

1) test all dtypes
2) check against the promotion table
3) remove checking the limits (value-based casting?)

Author: ev-br

array_api_tests/test_data_type_functions.py

@@ -19,18 +19,10 @@ def non_complex_dtypes():
     return xps.boolean_dtypes() | hh.real_dtypes
 
 
-def numeric_dtypes():
-    return xps.boolean_dtypes() | hh.real_dtypes | hh.complex_dtypes
-
-
 def float32(n: Union[int, float]) -> float:
     return struct.unpack("!f", struct.pack("!f", float(n)))[0]
 
 
-def _float_match_complex(complex_dtype):
-    return xp.float32 if complex_dtype == xp.complex64 else xp.float64
-
-
 @given(
     x_dtype=non_complex_dtypes(),
     dtype=non_complex_dtypes(),
@@ -115,46 +107,23 @@ def test_broadcast_to(x, data):
     # TODO: test values
 
 
-@given(_from=numeric_dtypes(), to=numeric_dtypes(), data=st.data())
-def test_can_cast(_from, to, data):
-    from_ = data.draw(
-        st.just(_from) | hh.arrays(dtype=_from, shape=hh.shapes()), label="from_"
-    )
+@given(_from=hh.all_dtypes, to=hh.all_dtypes)
+def test_can_cast(_from, to):
+    out = xp.can_cast(_from, to)
 
-    out = xp.can_cast(from_, to)
+    expected = False
+    for other in dh.all_dtypes:
+        if dh.promotion_table.get((_from, other)) == to:
+            expected = True
+            break
 
     f_func = f"[can_cast({dh.dtype_to_name[_from]}, {dh.dtype_to_name[to]})]"
-    assert isinstance(out, bool), f"{type(out)=}, but should be bool {f_func}"
-    if _from == xp.bool:
-        expected = to == xp.bool
-    else:
-        same_family = None
-        for dtypes in [dh.all_int_dtypes, dh.real_float_dtypes, dh.complex_dtypes]:
-            if _from in dtypes:
-                same_family = to in dtypes
-                break
-        assert same_family is not None  # sanity check
-        if same_family:
-            from_dtype = (_float_match_complex(_from)
-                          if _from in (xp.complex64, xp.complex128)
-                          else _from)
-            to_dtype = (_float_match_complex(to)
-                        if to in (xp.complex64, xp.complex128)
-                        else to)
-
-            from_min, from_max = dh.dtype_ranges[from_dtype]
-            to_min, to_max = dh.dtype_ranges[to_dtype]
-            expected = from_min >= to_min and from_max <= to_max
-        else:
-            expected = False
     if expected:
         # cross-kind casting is not explicitly disallowed. We can only test
-        # the cases where it should return True. TODO: if expected=False,
-        # check that the array library actually allows such casts.
+        # the cases where it should return True.
         assert out == expected, f"{out=}, but should be {expected} {f_func}"
 
 
-
 @pytest.mark.parametrize("dtype", dh.real_float_dtypes)
 def test_finfo(dtype):
     out = xp.finfo(dtype)