Add unittest

Add unittest

[   16s] + ./rustc_version
[   16s]
[   16s] running 28 tests
[   16s] test parse_1_0_0 ... ok
[   16s] test parse_1_16_0_nightly ... ok
[   16s] test parse_1_47_0_stable ... ok
[   16s] test parse_debian_buster ... ok
[   16s] test parse_llvm_micro ... ok
[   16s] test parse_llvm_version_11 ... ok
[   16s] test parse_llvm_version_11_0 ... ok
[   16s] test parse_llvm_version_3 ... ok
[   16s] test parse_llvm_version_3_0 ... ok
[   16s] test parse_llvm_version_3_9 ... ok
[   16s] test parse_llvm_version_4_0 ... ok
[   16s] test parse_llvm_version_4_components ... ok
[   16s] test parse_llvm_version_5 ... ok
[   16s] test parse_llvm_version_5_0 ... ok
[   16s] test parse_llvm_version_component_sign_minus ... ok
[   16s] test parse_llvm_version_component_sign_plus ... ok
[   16s] test parse_llvm_version_empty ... ok
[   16s] test parse_llvm_version_invalid_char ... ok
[   16s] test parse_llvm_version_leading_zero_on_nonzero ... ok
[   16s] test parse_llvm_version_leading_zero_on_zero ... ok
[   16s] test parse_llvm_version_overflow ... ok
[   16s] test parse_nightly ... ok
[   16s] test parse_termux ... ok
[   16s] test parse_stable ... ok
[   16s] test parse_unknown ... ok
[   16s] test test_llvm_version_comparison ... ok
[   16s] test rustc_error ... ok
[   17s] test smoketest ... ok
[   17s]
[   17s] test result: ok. 28 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.39s