Add tests

[adnan360]

Add tests based on bats, a TAP-compliant testing framework for bash. Requires: bats package (available on Debian/Arch repos) and then tests/run.sh to run the tests (instructions on readme as well).

Should fix #10

Example output:

1..15
ok 1 Single brackets test
ok 2 Single brackets with basic math test
ok 3 Exponent in bracket with math test
not ok 4 2 levels of brackets test
# (in test file tests/pemdas.bats, line 22)
#   `[ "$result" -eq 6 ]' failed
not ok 5 3 levels of brackets test
# (in test file tests/pemdas.bats, line 27)
#   `[ "$result" -eq 8 ]' failed
ok 6 Multiple digits without bracket first test
ok 7 Multiple digits without bracket second test
ok 8 Multiple digits with bracket and operations test
ok 9 Addition test
ok 10 Subtraction test
ok 11 Multiplication test
ok 12 Division test
ok 13 Division with remainder test
ok 14 Exponent test
ok 15 Decimal not supported error test

The 2 failed tests are due to this which will probably be fixed soon and it will pass.

[adnan360]

Closing this since bash based testing system is working fine and can do the same thing without dependencies.