add: unit and integration testing

app/node_modules/detect-newline/index.d.ts

@@ -0,0 +1,26 @@
+declare const detectNewline: {
+	/**
+	Detect the dominant newline character of a string.
+
+	@returns The detected newline or `undefined` when no newline character is found.
+
+	@example
+	```
+	import detectNewline = require('detect-newline');
+
+	detectNewline('foo\nbar\nbaz\r\n');
+	//=> '\n'
+	```
+	*/
+	(string: string): '\r\n' | '\n' | undefined;
+
+	/**
+	Detect the dominant newline character of a string.
+
+	@returns The detected newline or `\n` when no newline character is found or the input is not a string.
+	*/
+	graceful(string: string): '\r\n' | '\n';
+	graceful(string?: unknown): '\n';
+};
+
+export = detectNewline;