docs: mention pytest.approx in Assertions guide

Author: tanuj-rai

doc/en/how-to/assert.rst

@@ -66,6 +66,32 @@ See :ref:`assert-details` for more information on assertion introspection.
 
 .. _`assertraises`:
 
+Assertions about approximate equality
+-------------------------------------
+
+When comparing floating point values (or arrays of floats), small rounding
+errors are common. Instead of using ``assert abs(a - b) < tol`` or
+``numpy.isclose``, you can use :func:`pytest.approx`:
+
+.. code-block:: python
+
+    import pytest
+    import numpy as np
+
+    def test_floats():
+        assert (0.1 + 0.2) == pytest.approx(0.3)
+
+    def test_arrays():
+        a = np.array([1.0, 2.0, 3.0])
+        b = np.array([0.9999, 2.0001, 3.0])
+        assert a == pytest.approx(b)
+
+``pytest.approx`` works with scalars, lists, dictionaries, and NumPy arrays.
+It also supports comparisons involving NaNs.
+
+See :ref:`approx` for details.
+
+
 Assertions about expected exceptions
 ------------------------------------------