sh - busybox shell error: line 9 (left square bracket): not found

Question

I have the following code and I get the Error "line 9: [: not found":

#!/bin/sh
msg=$(dmesg | tail -n1)
echo "$msg"
if [ "$msg" = "Tasklet grp12" ]
then
    echo "Test was successful, Strings are equal."
else
    echo "Test failed, Strings are not equal."
fi

Answer 1

thanks to Charles Duffy! I had to check the box "Builtin version of 'test'" in the shell section of the make menuconfig menu of busybox, to enable string comparison. Now the code works. Since I had grep activated I first tried another solution which also worked but has a bad performance for sure:

#!/bin/sh
msg=$(dmesg | tail -n1)
echo "$msg"
tasklet="Tasklet grp12"
if ( echo "$msg" | grep "^$tasklet$" )
then
    echo "Test was successful, Strings are equal."
else
    echo "Test failed, Strings are not equal."
fi