def before$\_$space$($s$)$:

$"""$

Returns the substring of s up to$,$ but not including, the first space.

Example: before$\_$space$(\text{'}$Hello World'$)$ returns 'Hello'

Parameter s: the string to slice

Precondition: s is a string with at least one space in it

$"""$

Reread the specification for before$\_$space, paying close attention to the precondition. Create test cases for this function and add them to the test procedure test$\_$before$\_$space in testcurrency.py$.$ Remember, to implement a test case:

Call the function on a sample input of your choice.

Store the returned result as a variable.

Compare the result with the expected output using assert$\_$equals in introcs.

See the Unit Test Functions in the IntroCS API for more information.

When designing test cases for before$\_$space, think about how spaces may occur in the string $$ both position and frequency $$ and how that can affect the result.