TST: fixed eng_formatter doctest for #42671

ci/code_checks.sh

@@ -121,7 +121,8 @@ if [[ -z "$CHECK" || "$CHECK" == "doctests" ]]; then
       pandas/io/parsers/ \
       pandas/io/sas/ \
       pandas/io/sql.py \
-      pandas/tseries/
+      pandas/tseries/ \
+      pandas/io/formats/format.py
     RET=$(($RET + $?)) ; echo $MSG "DONE"
 
 fi

pandas/io/formats/format.py

@@ -1956,7 +1956,7 @@ def __call__(self, num: int | float) -> str:
         """
         Formats a number in engineering notation, appending a letter
         representing the power of 1000 of the original number. Some examples:
-
+        >>> format_eng = EngFormatter()
         >>> format_eng(0)       # for self.accuracy = 0
         ' 0'
 
@@ -1983,6 +1983,9 @@ def __call__(self, num: int | float) -> str:
             return "inf"
 
         sign = 1
+        if dnum == 0:
+            formatted = ' 0'
+            return formatted
 
         if dnum < 0:  # pragma: no cover
             sign = -1