Fix for cypress-io#7818 - cy.route swallows error message when fixtur…

…e does not exist

packages/driver/cypress/integration/commands/fixtures_spec.js

@@ -50,6 +50,10 @@ describe('src/cy/commands/fixtures', () => {
       cy.fixture('example').should('deep.eq', { example: true })
     })
 
+    it('works with null.json', () => {
+      cy.fixture('null.json').should('equal', null)
+    })
+
     it('can read a fixture without extension with multiple dots in the name', () => {
       cy.fixture('foo.bar.baz').should('deep.eq', { quux: 'quuz' })
     })

packages/driver/cypress/integration/commands/xhr_spec.js

@@ -2122,6 +2122,17 @@ describe('src/cy/commands/xhr', () => {
         .wrap({ foo: 'bar' }).as('foo')
         .route(/foo/, '@bar')
       })
+
+      it('throws when fixture cannot be found', () => {
+        cy.on('fail', (err) => {
+          expect(err.message).to.contains('A fixture file could not be found at any of the following paths:')
+        })
+
+        cy.route(/foo/, 'fx:NOT_EXISTING_FILE_FIXTURE')
+        cy.window().then((win) => {
+          win.$.get('/foo')
+        })
+      })
     })
 
     describe('.log', () => {

packages/driver/src/cy/commands/fixtures.js

@@ -58,7 +58,7 @@ module.exports = (Commands, Cypress, cy, state, config) => {
       return Cypress.backend('get:fixture', fixture, _.pick(options, 'encoding'))
       .timeout(timeout)
       .then((response) => {
-        const err = response.__error
+        const err = response?.__error
 
         if (err) {
           return $errUtils.throwErr(err)

packages/driver/src/cy/commands/xhr.js

@@ -200,7 +200,7 @@ const startXhrServer = (cy, state, config) => {
     },
 
     onFixtureError (xhr, err) {
-      err = $errUtils.cypressErr(err)
+      err = $errUtils.cypressErr({ message: err })
 
       return this.onError(xhr, err)
     },
@@ -471,6 +471,13 @@ module.exports = (Commands, Cypress, cy, state, config) => {
           })
         }
 
+        // look ahead to see if fixture exists
+        const fixturesRe = /^(fx:|fixture:)/
+
+        if (hasResponse && fixturesRe.test(options.response)) {
+          return cy.fixture(options.response.replace(fixturesRe, '')).then(() => route())
+        }
+
         return route()
       }