function assert( t, fixture, done ) {
	var expression;
	var expected;
	var istream;
	var opts;
	var r;

	istream = new DebugStream({
		'name': 'repl-input-stream'
	});
	opts = {
		'input': istream,
		'inputPrompt': '',
		'quiet': true,
		'settings': defaultSettings()
	};
	r = repl( opts, onClose );

	// Load test theme:
	r.addTheme( 'test', fixture.theme );
	r.settings( 'theme', 'test' );

	// Get expression and expected strings:
	expression = fixture.expression;
	expected = fixture.expected;

	// Emulate the presence of an existing expression:
	istream.write( expression );

	// Close the input stream:
	istream.end();

	// Close the REPL:
	r.close();

	function onClose( error, data ) {
		var actual;
		if ( error ) {
			t.fail( error.message );
			return;
		}
		actual = data[ data.length - 1 ];
		t.strictEqual( actual, expected, 'returns expected value' );
		done();
	}
}
Asserts that a provided expression triggers expected syntax highlighting.

@private
@param {Object} t - test object
@param {Object} fixture - fixture object
@param {string} fixture.expression - expression string
@param {string} fixture.expected - expected/highlighted string
@param {Object} fixture.theme - test theme
@param {Function} done - callback to invoke upon completion