Gitlab CI : Modify artifacts between jobs

I’m starting with Gitlab and gitlab CI and my first gitlab-ci is not working as expecting :

I created 3 jobs in 3 differents stages to :
1° create a file
2° modify the file
3° test the content of the file
1° and 2° are doing what I expect but the file tested in step3 seems to be the empty file created in 1° and not the file modified in step 2°.

My gitlab-ci.yaml :

- prep
- build
- test

prepare the car:
stage: prep
- mkdir build
- cd build
- touch car.txt
- build/

build the car:
stage: build
- cd build
- echo “Chassis” >> car.txt
- echo “Engine” >> car.txt
- echo “Wheels” >> car.txt
- cat car.txt
- build/

test the car:
stage: test
- ls
- test -f build/car.txt
- cd build
- grep “Chassis” car.txt
- grep “Engine” car.txt
- grep “Wheels” car.txt

I also tried to not declare again the artifacts in the ‘build the car’ job but the result is still the same : ‘test the car’ failed at grep "Chassis" car.txt because car.txt is empty.

Thanks by advance.