Add readable, writable and duplex

test/isReadableStream/isReadableStream.js

@@ -0,0 +1,7 @@
+const isReadableStream = val =>
+  val !== null &&
+  typeof val === 'object' &&
+  typeof val.pipe === 'function' &&
+  typeof val._read === 'function' &&
+  typeof val._readableState === 'object';
+module.exports = isReadableStream;

test/isReadableStream/isReadableStream.test.js

@@ -0,0 +1,20 @@
+const expect = require('expect');
+const isReadableStream = require('./isReadableStream.js');
+const fs = require('fs');
+const Stream = require('stream');
+
+test('isReadableStream is a Function', () => {
+  expect(isReadableStream).toBeInstanceOf(Function);
+});
+test('isReadableStream returns true for read streams', () => {
+  expect(isReadableStream(fs.createReadStream('isReadableStream.js'))).toBeTruthy();
+});
+test('isReadableStream returns false for write streams', () => {
+  expect(isReadableStream(fs.createWriteStream('isReadableStream.js'))).toBeFalsy();
+});
+test('isReadableStream returns true for duplex streams', () => {
+  expect(isReadableStream(new Stream.Duplex())).toBeTruthy();
+});
+test('isReadableStream returns false for non-streams', () => {
+  expect(isReadableStream({})).toBeFalsy();
+});