TST: add a test that wrapping preserves a view/copy semantics for unary functions

If a bare library returns a copy, so does the wrapped library; if the bare
library returns a view, so does the wrapped library.

Author: ev-br

tests/test_copies_or_views.py

@@ -0,0 +1,66 @@
+"""
+A collection of tests to make sure that wrapped namespaces agree with the bare ones
+on whether to return a view or a copy of inputs.
+"""
+import pytest
+from ._helpers import import_
+
+
+LIB_NAMES = ['numpy', 'cupy', 'torch', 'dask.array', 'array_api_strict']
+
+FUNC_INPUTS = [
+    # func_name, arr_input, dtype,  scalar_value
+    ('abs', [1, 2], 'int8', 3),
+    ('abs', [1, 2], 'float32', 3.),
+    ('ceil', [1, 2], 'int8', 3),
+    ('clip', [1, 2], 'int8', 3),
+    ('conj', [1, 2], 'int8', 3),
+    ('floor', [1, 2], 'int8', 3),
+    ('imag', [1j, 2j], 'complex64', 3),
+    ('positive', [1, 2], 'int8', 3),
+    ('real', [1., 2.], 'float32', 3.),
+    ('round', [1, 2], 'int8', 3),
+    ('sign', [0, 0], 'float32', 3),
+    ('trunc', [1, 2], 'int8', 3),
+    ('trunc', [1, 2], 'float32', 3),
+]
+
+
+def ensure_unary(func, arr):
+    """Make a trivial unary function from func."""
+    if func.__name__ == 'clip':
+        return lambda x: func(x, arr[0], arr[1])
+    return func
+
+
+def is_view(func, a, value):
+    """Apply `func`, mutate the output; does the input change?"""
+    b = func(a)
+    b[0] = value
+    return a[0] == value
+
+
+@pytest.mark.parametrize('xp_name', LIB_NAMES) 
+@pytest.mark.parametrize('inputs', FUNC_INPUTS, ids=[inp[0] for inp in FUNC_INPUTS])
+def test_view_or_copy(inputs, xp_name):
+    bare_xp = import_(xp_name, wrapper=False)
+    wrapped_xp = import_(xp_name, wrapper=True)
+
+    func_name, arr_input, dtype_str, value = inputs
+    dtype = getattr(bare_xp, dtype_str)
+
+    bare_func = getattr(bare_xp, func_name)
+    bare_func = ensure_unary(bare_func, arr_input)
+
+    wrapped_func = getattr(wrapped_xp, func_name)
+    wrapped_func = ensure_unary(wrapped_func, arr_input)
+
+    # bare namespace: mutate the output, does the input change?
+    a = bare_xp.asarray(arr_input, dtype=dtype)
+    is_view_bare = is_view(bare_func, a, value)
+
+    # wrapped namespace: mutate the output, does the input change?
+    a1 = wrapped_xp.asarray(arr_input, dtype=dtype)
+    is_view_wrapped = is_view(wrapped_func, a1, value)
+
+    assert is_view_bare == is_view_wrapped