TST: Add docstrings to arithmetic fixtures (pandas-dev#29441)

Author: dalgarno

pandas/tests/arithmetic/conftest.py

@@ -21,7 +21,24 @@ def id_func(x):
 
 @pytest.fixture(params=[1, np.array(1, dtype=np.int64)])
 def one(request):
-    # zero-dim integer array behaves like an integer
+    """
+    Several variants of integer value 1. The zero-dim integer array
+    behaves like an integer.
+
+    This fixture can be used to check that datetimelike indexes handle
+    addition and subtraction of integers and zero-dimensional arrays
+    of integers.
+
+    Examples
+    --------
+    >>> dti = pd.date_range('2016-01-01', periods=2, freq='H')
+    >>> dti
+    DatetimeIndex(['2016-01-01 00:00:00', '2016-01-01 01:00:00'],
+    dtype='datetime64[ns]', freq='H')
+    >>> dti + one
+    DatetimeIndex(['2016-01-01 01:00:00', '2016-01-01 02:00:00'],
+    dtype='datetime64[ns]', freq='H')
+    """
     return request.param
 
 
@@ -40,8 +57,21 @@ def one(request):
 
 @pytest.fixture(params=zeros)
 def zero(request):
-    # For testing division by (or of) zero for Index with length 5, this
-    # gives several scalar-zeros and length-5 vector-zeros
+    """
+    Several types of scalar zeros and length 5 vectors of zeros.
+
+    This fixture can be used to check that numeric-dtype indexes handle
+    division by any zero numeric-dtype.
+
+    Uses vector of length 5 for broadcasting with `numeric_idx` fixture,
+    which creates numeric-dtype vectors also of length 5.
+
+    Examples
+    --------
+    >>> arr = pd.RangeIndex(5)
+    >>> arr / zeros
+    Float64Index([nan, inf, inf, inf, inf], dtype='float64')
+    """
     return request.param