Comparing special characters in Bash - bash

Question

I have a function I have written that outputs coloured output kind of like this:
foo() {
local arrow="\033[1;32m↑\033[0m"
echo "1$arrow"
}
I'd like to test this function so I'm using https://github.com/kward/shunit2 to do unit tests for it.
test_foo() {
local green_arrow="\033[1;32m↑\033[0m"
assertEquals "1$green_arrow" "$(foo)"
}
But shunit complains that: ASSERT:expected:< 1↑> but was:< 1↑>. I'm guessing there's a problem with hidden characters being output by the function.
Is there any way to strip special characters, or escape them from the variable?
Edit:
Running the following commands shows that the \\033 escape character is being converted, probably by echo, into a literal \E escape:
printf '%q' "1$green_arrow"
' 1\\033[1;32m?\206\221\\033[0m'
printf '%q' "$(foo)"
' 1\E[1;32m?\206\221\E[0m'

Answer 1

Using printf -v varname_quoted %q "$varname" to get escaped forms of your content will provide an easier-to-read and easy-to-reason-about form, which can also be included in your code as literals with no additional quoting or escaping needed. (This can be simplified to printf %q "$varname" if your goal is to emit quoted content to stdout, rather than to another variable).
That is to say, to get a format string to a literal (with support in the format string for arguments, ie. %s, %02f, etc):
printf -v green_arrow '\033[1;32m↑\033[0m'
...or, a backslash-escaped string (which supports only a subset of full format-string syntax) to a literal:
printf -v green_arrow '%b' '\033[1;32m↑\033[0m'
...and then, to get that literal emitted in escaped, human-readable form for easy comparison and/or copy-and-paste into shell scripts as a literal:
printf '%q\n' "$green_arrow"
Tying this all together, the following is one way to get a more readable error message (please pardon StackOverflow's syntax highlighting, which as of this writing doesn't fully grok the way nested quoting contexts work in bash):
test_foo() {
local green_arrow=$'\E[1;32m↑\E[0m'
assertEquals "$(printf '%q' " 1$green_arrow")" "$(printf '%q' "$(foo)")"
}
...or, more efficiently (avoiding the unnecessary subshells):
test_foo() {
local green_arrow=$'\E[1;32m↑\E[0m'
local desired_answer_quoted actual_answer_quoted
printf -v desired_answer_quoted '%q' " 1$green_arrow"
printf -v actual_answer_quoted '%q' "$(foo)"
assertEquals "$desired_answer_quoted" "$actual_answer_quoted"
}