add: unit and integration testing

app/node_modules/detect-newline/index.js

@@ -0,0 +1,21 @@
+'use strict';
+
+const detectNewline = string => {
+	if (typeof string !== 'string') {
+		throw new TypeError('Expected a string');
+	}
+
+	const newlines = string.match(/(?:\r?\n)/g) || [];
+
+	if (newlines.length === 0) {
+		return;
+	}
+
+	const crlf = newlines.filter(newline => newline === '\r\n').length;
+	const lf = newlines.length - crlf;
+
+	return crlf > lf ? '\r\n' : '\n';
+};
+
+module.exports = detectNewline;
+module.exports.graceful = string => (typeof string === 'string' && detectNewline(string)) || '\n';