Python: How to remove part of a string starting at a keyword for multiple lines?

Here is my code:

with open('locations.txt', 'r') as f, open('output.txt', 'w') as fo:
for line in f:
    fo.write(line.replace('test'[:-1], ''))

I have a file with multiple lines of text:

This is a test the cat jumped around
This is another test the dog jumped under
This is a third test the cow jumped over

I want to be able to open the text file, and remove everything on each line after the word 'test'. So result would look like:

This is a test
This is another test
This is a third test

I am trying to use .replace() but using the paramter of -1 it just removed everything but the last letter in test. I am really not sure how to have the word 'test' be the input then have it remove the rest of the string after that on each line.

Solution

use regex to find where "test" first appears in your string

with open('locations.txt', 'r') as f, open('output.txt', 'w') as fo:
    for line in f:
        index = re.search("test",line).span()[1]
        fo.write(line[:index ])

heres a breakdown:

re.search("test",line) searches for "test" in line

re.search("test",line).span() returns a tuple with the starting position and the ending position of what you wanted to find ("test")

re.search("test",line).span()[1] gives you the ending position of the word "test" in the line

finally line[:index ] gives you a slice of line up until the ending position of where it found "test"