Fix silent test failures enforcing min shunit2 version

[arthurbdiniz]

This pull request addresses silent test failures due to an outdated version of shunit2. It introduces a compatibility check to ensure that shunit2 version 2.1.8 or higher is installed before running the tests.

If the required version is not met, an informative error message is displayed, guiding users on how to resolve the issue.

A new script file compatibility.sh has been added to perform this check, and tests.sh now calls this script at the start to enforce the minimum version requirement.

Validation

1. Environment running version 2.1.6

podman run -v `pwd`:/home -w /home -it ubuntu:jammy bash
apt update && apt install -y curl shunit2
./tests/tests.sh

Error: shunit2 version 2.1.8 or higher is required.
Please install a compatible version of shunit2.

2. Environment running version 2.1.8

./tests/tests.sh 
testUsage
testNoOptionError
testInvalidOptionError
testParallelIfMoreThanOneUrl
testEncodingWhitespace
testDoubleDash
testCurlOptions
testNextAmount
testUrlStartingWithDash
testOutputFileName
testOutputFileNameRepeatedOption
testUrlDefaultName
testUrlDefaultNameTrailingSlash
testUrlDecodingWhitespaces
testUrlDecodingWhitespacesTwoFiles
testUrlDecodingDisabled
testUrlDecodingWhitespacesQueryString
testUrlDecodingWhitespacesTrailingSlash
testUrlDecodingNonLatinLanguages

Ran 19 tests.

OK

Closes: #39

[samueloph]

As we discussed in person, you can simplify all of this by directly calling assertContains in the if statement and branching on the result of that.

This might expose the issue with macos, which is currently failing for an unknown reason.