finfo_test: improve min/max test

ml_dtypes/tests/finfo_test.py

@@ -12,22 +12,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import contextlib
-import warnings
-
 from absl.testing import absltest
 from absl.testing import parameterized
 import ml_dtypes
 import numpy as np
 
-
-@contextlib.contextmanager
-def ignore_warning(**kw):
-  with warnings.catch_warnings():
-    warnings.filterwarnings("ignore", **kw)
-    yield
-
-
 ALL_DTYPES = [
     ml_dtypes.bfloat16,
     ml_dtypes.float8_e4m3b11,
@@ -76,11 +65,11 @@ def assert_representable(val):
       self.assertEqual(make_val(val).item(), val)
 
     def assert_infinite(val):
-      typed_val = make_val(val)
-      if typed_val.dtype in DTYPES_WITH_NO_INFINITY:
-        self.assertTrue(np.isnan(typed_val))
+      val = make_val(val)
+      if dtype in DTYPES_WITH_NO_INFINITY:
+        self.assertTrue(np.isnan(val), f"expected NaN, got {val}")
       else:
-        self.assertTrue(np.isposinf(typed_val))
+        self.assertTrue(np.isposinf(val), f"expected inf, got {val}")
 
     def assert_zero(val):
       self.assertEqual(make_val(val), make_val(0))
@@ -92,13 +81,12 @@ def assert_zero(val):
     self.assertEqual(info.nmant + info.nexp + 1, info.bits)
 
     assert_representable(info.tiny)
+
     assert_representable(info.max)
-    assert_representable(info.min)
+    assert_infinite(np.spacing(info.max))
 
-    msg = "overflow encountered in nextafter"
-    with ignore_warning(category=RuntimeWarning, message=msg):
-      assert_infinite(np.nextafter(info.max, make_val(np.inf)))
-      assert_infinite(-np.nextafter(info.min, make_val(-np.inf)))
+    assert_representable(info.min)
+    assert_infinite(-np.spacing(info.min))
 
     assert_representable(2.0 ** (info.maxexp - 1))
     assert_infinite(2.0**info.maxexp)