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Now, when we speak about automated testing,

it is important to understand that there are different kinds

of automated tests which you can have a look at.

For example, there are unit tests and I can already say

that those will be super important.

But you also have so-called integration tests

and end to end tests.

Now, these are the three main categories of tests

which you can write.

Unit tests are all about writing tests

for the smallest possible units off your application.

So for functions, individual functions that you use

in your application.

Or in case of React apps,

testing some components independently

from the other components in your app.

And therefore projects typically contain a lot

of unit tests, since you basically wanna test

all the units, all the functions and components

that make up your application.

And hence this is the most common

and important kind of test.

And the idea simply is that

if you test all the individual units on themselves,

the overall application will also work.

But to verify that the overall application really works

if you put together all those units,

we have integration tests.

Here, we test the combination of multiple building blocks.

For example, multiple components working together.

And projects typically contain

a couple of such integration tests,

but not as many as you have unit tests.

Though as you will also see throughout this course section,

it's not always that easy to differentiate

between unit and integration tests when testing React apps,

since very often, you wanna test a component

that also uses some other component.

But we're going to see that in action

throughout this course section.

So generally, integration tests are also extremely important

but we have fewer integration tests than we have unit tests.

And then we also have end to end tests.

These are all about testing entire workflows

in your application, you could say.

Entire scenarios, like logging a user in

and then going to a certain page.

So these aim to really reproduce what a real human would do

with your website.

Basically what you would also do with manual testing,

just automated.

Now, whilst this might sound like the most important test

it definitely is important

and you therefore typically do write some end to end tests

but not as many as you have unit and integration tests,

because if your a unit and integration tests work,

you can be pretty sure that your overall application works.

And then those unit and integration tests

are simply easier to test.

They often are quicker to run and they are more focused

and it's way easier to test all possible scenarios,

if you test all your units for different scenarios

then coming up with all possible scenarios,

if you look at your app as a whole,

which is what you do typically with end to end tests.

So these are important,

but it's basically all to what you do manually

and therefore you have fewer of those tests.

Now in this course section, since it's an introduction

to testing.

We will focus on those most important kinds

of tests.

Unit tests and also to some extent integration tests.

But at the end of the module, I will also point you

at some other resources, which you can check out

to dive deeper into React testing if you want to.