Add initial ModuleCache spec

spec/module-cache-spec.coffee

@@ -0,0 +1,10 @@
+path = require 'path'
+Module = require 'module'
+
+describe 'ModuleCache', ->
+  beforeEach ->
+    spyOn(Module, '_findPath').andCallThrough()
+
+  it 'resolves atom shell module paths without hitting the filesystem', ->
+    require.resolve('shell')
+    expect(Module._findPath.callCount).toBe 0