Throw error on this.slow() informing users about slowTestThreshold in…

…side tests, hooks and suites.

packages/driver/src/cypress/error_messages.ts

@@ -892,6 +892,11 @@ export default {
 
     https://on.cypress.io/test-retries
     `,
+    manually_set_slow: stripIndent`\
+    Mocha \`this.slow()\` syntax is not supported.
+
+    The slow threshold can only be configured globally by \`slowTestThreshold\`. See https://on.cypress.io/configuration#Global
+    `,
     hook_registered_late: stripIndent`\
     Cypress detected you registered a(n) \`{{hookTitle}}\` hook while a test was running (possibly a hook nested inside another hook). All hooks must be registered before a test begins executing.
 

packages/driver/src/cypress/mocha.ts

@@ -27,6 +27,8 @@ const suiteAddTest = Suite.prototype.addTest
 const suiteAddSuite = Suite.prototype.addSuite
 const suiteRetries = Suite.prototype.retries
 const hookRetries = Hook.prototype.retries
+const suiteSlow = Suite.prototype.slow
+const hookSlow = Suite.prototype.slow
 const suiteBeforeAll = Suite.prototype.beforeAll
 const suiteBeforeEach = Suite.prototype.beforeEach
 const suiteAfterAll = Suite.prototype.afterAll
@@ -200,6 +202,14 @@ const restoreSuiteRetries = () => {
   Suite.prototype.retries = suiteRetries
 }
 
+const restoreSuiteSlow = () => {
+  Suite.prototype.slow = suiteSlow
+}
+
+const restoreHookSlow = () => {
+  Suite.prototype.slow = hookSlow
+}
+
 const restoreTestClone = () => {
   Test.prototype.clone = testClone
 }
@@ -264,6 +274,24 @@ const patchHookRetries = () => {
   }
 }
 
+const patchSuiteSlow = () => {
+  Suite.prototype.slow = function (...args) {
+    // Mocha calls this.slow() internally to set the default value of 75ms
+    // Any other value, we assume it's a user and inform them that this is doesn't actually do anything
+    if (args[0] !== undefined && args[0] !== 75) {
+      throw $errUtils.cypressErrByPath('mocha.manually_set_slow')
+    }
+  }
+}
+
+const patchHookSlow = () => {
+  Hook.prototype.slow = function (...args) {
+    if (args[0] !== undefined && args[0] !== 75) {
+      throw $errUtils.cypressErrByPath('mocha.manually_set_slow')
+    }
+  }
+}
+
 // matching the current Runner.prototype.fail except
 // changing the logic for determing whether this is a valid err
 const patchRunnerFail = () => {
@@ -378,6 +406,10 @@ const patchSuiteAddTest = (specWindow, config) => {
       return testRetries.apply(this, args)
     }
 
+    test.slow = function () {
+      throw $errUtils.cypressErrByPath('mocha.manually_set_slow')
+    }
+
     return ret
   }
 }
@@ -468,6 +500,8 @@ const restore = () => {
   restoreRunnableResetTimeout()
   restoreSuiteRetries()
   restoreHookRetries()
+  restoreSuiteSlow()
+  restoreHookSlow()
   restoreRunnerRunTests()
   restoreTestClone()
   restoreSuiteAddTest()
@@ -482,6 +516,8 @@ const override = (specWindow, Cypress, config) => {
   patchRunnableResetTimeout()
   patchSuiteRetries()
   patchHookRetries()
+  patchSuiteSlow()
+  patchHookSlow()
   patchRunnerRunTests()
   patchTestClone()
   patchSuiteAddTest(specWindow, config)