feat(assertString): verifies that a value is a string

assertString.js

@@ -0,0 +1,26 @@
+/* @flow */
+
+const assert = require('./assert')
+const isString = require('lodash/isString')
+
+/**
+ * verifies that `actual` is a string
+ *
+ * @throws {AssertionError} test failure
+ * @example
+ * import assertString from 'secondwheel/assertString'
+ *
+ * describe('assertString', () => {
+ *   it('should be a string', () => {
+ *     assertString('')
+ *   })
+ * })
+ */
+const assertString = (
+  actual/*: any */,
+  message/*:: ?:string */ = 'expected value to be a string'
+) => {
+  assert(actual, isString, message)
+}
+
+module.exports = assertString