I am attempting to use the Intern test framework to automate testing of a simple REST API implemented with node.js and StrongLoop. StrongLoop provides an explorer web page
Intern runs its tests in an AMD environment, so require is the AMD loader's require, not Node's, hence your error.
To load Node modules, use the intern/dojo/node! AMD plugin and include them in your module's dependencies, e.g.:
define([
    ...,
    'intern/dojo/node!http'
], function (..., http) {
    // Now http contains the exports of Node's http module
});
This is documented in Intern's User Guide under Testing CommonJS Modules.