Missing tests for ANSI formatting and NO_COLOR

[ericcornelissen]

Test Improvements

Caused by #13
Relates to #5, #16

Summary

The original no_colors.rs test did not function correctly (removing/commenting out the line cmd.env("NO_COLOR", "1"); did not change test outcomes). A new test suite should be created to validate the behavior of the CLI when it comes to ANSI styling and various conditions that affect it (such as the NO_COLOR environment variable).

Suggestion

The following general test outline is recommended based on current knowledge (tests/ansi_test.rs):

// SPDX-License-Identifier: Apache-2.0

//! Test suite focussed on testing that ANSI is or isn't used in stdout/stderr based on options to
//! suppress ansi-formatting.

pub mod common;

use crate::common::TestResult;

use predicates::prelude::*;

#[test]
fn example_test_with_color() -> TestResult {
    with_color(|mut cmd, _test_dir| {
        cmd.arg("--help").assert().stdout(has_ansi());

        Ok(())
    })
}

#[test]
fn example_test_without_color() -> TestResult {
    without_color(|mut cmd, _test_dir| {
        cmd.arg("--help").assert().stdout(no_ansi()).stderr(no_ansi());

        Ok(())
    })
}

/// Run a test with ANSI styling enabled.
///
/// See also [`common::with_test_dir`].
fn with_color<C>(callback: C) -> TestResult
where
    C: FnOnce(assert_cmd::Command, &assert_fs::TempDir) -> TestResult,
{
    common::with_test_dir(|cmd, test_dir| callback(cmd, test_dir))
}

/// Run a test with the `NO_COLOR` environment variable set.
///
/// See also [`common::with_test_dir`].
fn without_color<C>(callback: C) -> TestResult
where
    C: FnOnce(assert_cmd::Command, &assert_fs::TempDir) -> TestResult,
{
    common::with_test_dir(|mut cmd, test_dir| {
        cmd.env("NO_COLOR", "1");
        callback(cmd, test_dir)
    })
}

/// Create a predicate that evaluates to `true` if a given string contains ANSI characters.
fn has_ansi() -> predicates::str::RegexPredicate {
    // This regular expression is based on based on (MIT licensed):
    // <https://github.com/TheLarkInn/ansi-regex>
    const ANSI_REGEX: &str = r"\x1b\[([\x30-\x3f]*[\x20-\x2f]*[\x40-\x7e])";

    predicates::str::is_match(ANSI_REGEX).expect("static regular expression should always be valid")
}

/// Create a predicate that evaluates to `true` if a given string does not contain ANSI characters.
fn no_ansi() -> predicates::boolean::NotPredicate<predicates::str::RegexPredicate, str> {
    has_ansi().not()
}