Append text at the beginning of lines in a file

I have a text file

cat file.txt

This is line1
This is line2
This is line3
This is line4.

My requirement is to append Test1 ,Test2 to the lines randomly.

Output should be as below.

Test1 This is line1
Test2 This is line2
Test1 This is line3
Test2 This is line4.