added intercept for error 500

cypress/fixtures/login_error.json

@@ -0,0 +1,7 @@
+{
+    "errors": {
+      "Error 500 -": [
+        "Internal server error"
+      ]
+    }
+}

cypress/integration/login.spec.js

@@ -1,6 +1,9 @@
 import login from '../selectors/login.sel'
+import header from '../selectors/header.sel'
 
 describe('Login', () => {
+    // context is the same as describe
+    context('unsuccessful', () => {
         beforeEach(() => {
             // visit ('/login') -> will visit baseUrl + /login
             // baseUrl is set in config - cypress.json file
@@ -15,10 +18,39 @@ describe('Login', () => {
                 .and('contain', 'email or password is invalid')
         })
 
-    it('can press enter to log in', () => {
+        it('can see error message when username and password fields are empty', () => {
+            cy.get(login.signInButton).click()
+            cy.get(login.errorMessages).should('be.visible')
+                .and('contain', 'email or password is invalid')
+        })
+
+        it('can see error message when API responds with 500', () => {
+            cy.intercept('POST', 'https://conduit.productionready.io/api/users/login', {
+                method: 'POST',
+                statusCode: 500,
+                fixture: 'login_error'
+            })
             cy.get(login.emailField).type('random2@test.com')
             cy.get(login.passwordField).type('random_pass{enter}')
             cy.get(login.errorMessages).should('be.visible')
-            .and('contain', 'email or password is invalid')
+                .and('contain', 'Error 500 - Internal server error')
+        })
+    })
+
+    context('successful', () => {
+        beforeEach(() => {
+            // we need a new user
+            cy.register().then((email) => {
+                cy.wrap(email).as('email')
+            })
+            cy.visit('/login')
+        })
+
+        it('can log in', function () {
+            cy.get(login.emailField).type(this.email)
+            cy.get(login.passwordField).type('Testtest1')
+            cy.get(login.signInButton).click()
+            cy.get(header.settingsLink).should('be.visible')
+        })
     })
 })