Add tests for `language-pack` command

[swissspidy]

Issue Overview

Especially needed because of this bug where $projects is immediately overridden, so using --all doesn't really work:

traduttore/inc/CLI/LanguagePackCommand.php

Lines 228 to 247 in a9faec1

	$projects = [];
	if ( $all ) {
	$projects = $this->get_all_projects();
	}
	$projects = array_map(
	function ( $project_id ) {
	$project = ( new ProjectLocator( $project_id ) )->get_project();
	if ( ! $project ) {
	WP_CLI::log( sprintf( 'Project (ID: %d) does not exist.', $project_id ) );
	return null;
	}
	if ( ! $project->is_active() ) {
	WP_CLI::log( sprintf( 'Project (ID: %d) is inactive.', $project->get_id() ) );
	return null;
	}
	return $project;
	},
	$args
	);

To Reproduce
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4. See error

Expected behavior
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Versions

• Browser:
• PHP:
• WP-CLI:
• GlotPress:
• WordPress:

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