add Cypress.sinon type (#6725)

cli/types/index.d.ts

@@ -207,6 +207,15 @@ declare namespace Cypress {
      *   new Cypress.Promise((resolve, reject) => { ... })
      */
     Promise: Bluebird.BluebirdStatic
+    /**
+     * Cypress includes Sinon.js library used in `cy.spy` and `cy.stub`.
+     *
+     * @see https://sinonjs.org/
+     * @see https://on.cypress.io/stubs-spies-and-clocks
+     * @see https://example.cypress.io/commands/spies-stubs-clocks
+     */
+    sinon: sinon.SinonApi
+
     /**
      * Cypress version string. i.e. "1.1.2"
      * @see https://on.cypress.io/version

cli/types/tests/cypress-tests.ts

@@ -13,6 +13,13 @@ namespace CypressMomentTests {
   Cypress.moment().startOf('week') // $ExpectType Moment
 }
 
+namespace CypressSinonTests {
+  Cypress.sinon // $ExpectType SinonApi
+  const stub = cy.stub()
+  stub(2, 'foo')
+  expect(stub).to.have.been.calledWith(Cypress.sinon.match.number, Cypress.sinon.match('foo'))
+}
+
 namespace CypressJqueryTests {
   Cypress.$ // $ExpectType JQueryStatic
   Cypress.$('selector') // $ExpectType JQuery<HTMLElement>