$ rename -n 's/tes*/file 1/' *
test-file-1 renamed as file 1t-file-1

$ rename -n 's/^*/file 1/' *
^* matches null string many times in regex; marked by <-- HERE in m/^* <-- HERE / at (eval 1) line 1.
example2 renamed as file 1example2
^* matches null string many times in regex; marked by <-- HERE in m/^* <-- HERE / at (eval 2) line 1.
test-file-1 renamed as file 1test-file-1
^* matches null string many times in regex; marked by <-- HERE in m/^* <-- HERE / at (eval 3) line 1.
third renamed as file 1third

$ rename -n 's/tes.*/file 1/' *
test-file-1 renamed as file 1

$ rename -n 's/.*/file 1/' *
example2 renamed as file 1
test-file-1 renamed as file 1
third renamed as file 1