The Complete React Developer Course (with Hooks and Redux) - Build It: Adding Total Selector

The video tutorial introduces a new feature for Expensify, focusing on creating an expense list header. The tutorial guides viewers through creating a selector function to sum expenses and writing test cases using Test Driven Development (TDD). It emphasizes the use of JavaScript methods like map and reduce, and demonstrates how to refactor code confidently with a robust test suite.

What is the primary purpose of the new expense list header feature in Expensify?

• To display the total number of expenses

• To summarize all visible expenses

• To categorize expenses by type

• To filter expenses by date

What is the main task in this video regarding the new feature?

• Implementing a new navigation bar

• Developing a selector function to sum expenses

• Designing a user interface

• Creating a new component

Which of the following is NOT a test case mentioned for the selector function?

• Should correctly add up multiple expenses

• Should correctly add up a single expense

• Should return 0 for no expenses

• Should handle negative expenses

What is the first step in setting up the files for the task?

• Creating a new component

• Setting up a selectors file and a test file

• Implementing a database connection

• Designing a new user interface

What is the main principle of test-driven development (TDD) introduced in the video?

• Skipping tests for faster development

• Using only manual testing

• Writing code before tests

• Writing tests before code

Which JavaScript methods are suggested for use in the function implementation?

• forEach and map

• reduce and filter

• map and reduce

• filter and sort

What is the purpose of using the reduce method in the function?

• To accumulate a total sum of expenses

• To iterate over expenses without modification

• To sort expenses by amount

• To filter out unwanted expenses

What is the benefit of having test cases in place when refactoring code?

• They make the code run faster

• They ensure the code is error-free

• They provide confidence that changes don't break functionality

• They automatically optimize the code

What is the expected outcome when passing an empty array to the selector function?

• The first expense in the list

• A null value

• A total of zero

• An error message

What is the next step after completing the function and test cases?

• Committing the changes

• Deploying the feature

• Displaying the information to the user

• Starting a new project