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you

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welcome to section 6 testing actors in

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the previous section working with akka

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cluster we were introduced to the occur

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Custer and touched upon topics such as

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remote actor rooting on the cluster

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cluster sharding and cluster singleton

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in this section we will shift our focus

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to testing different aspects of a cur we

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will test our actors parent-child

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relationships and finite state machines

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finally we will take a look at multimode

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tests let's start with the first video

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how to test an actor in this video we

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will take a look at the different styles

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to test the actor and we will start with

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coding acha comes with a dedicated

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module for supporting tests the akka

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test kit let's add the aqha test kit

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module and scarlett s to our

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dependencies here is the counter actor

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which handles the messages increment

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decrement and get count and has a count

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variable we want to implement our tests

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for this actor let's create a counter

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spec class that extends the test kit

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class which gives us the basic tools we

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need to work with actors this includes

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access to the actor system as well as

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helper methods for dealing with

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responses from actors under test we will

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be using Scala test in this video

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however it's possible to test occur

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using different testing frameworks the

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test kit provided by acha is test

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framework independent in case of Scala

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test we need to extend the flat spec

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like trait to get the general test

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syntax available before and after all to

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be able to hook into the Suites

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lifecycle events and we'll use the must

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matches to actually write our assertions

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using the X must do something style

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first let's shut down the actor system

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after all the tests finish for this

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override the after all method we will

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use the shutdown actor system method

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from test kit as our actor system was

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created by the test kit called system

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now let's add our test unit

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first let's define our sender actor that

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will send messages for our counter actor

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we will use test probes which allows us

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to send messages and expect response

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messages next let's define running an

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instance from our actor send an

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increment message and then get the count

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message now our sender should receive

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the response of the getcount message

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test probes provide some methods that

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help us to expect the messages let's use

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expect message type which expects a

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message of a specific type our response

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should be int if the sender receives a

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message with another type this

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expectation will fail finally let's

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assert on the value of the state the

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state must be equal to 1 let's run

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great it passes let's implement a test

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unit for increment messages only we do

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not want to set up a test probe each

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time in the test we can instead use the

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implicit senders trait which makes the

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test get able to receive messages

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directly the test kit contains the test

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actor which contains expectation methods

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such as test probe when we mix with

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implicit sender this test actor uses as

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a sender for any message in tests so

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let's define a running instance of a

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counter

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and send an increment message for it

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when the counter actor receives an

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increment message it just changes the

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count and doesn't send a response to the

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sender so let's expect that we didn't

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receive messages during that one second

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slot here we are using the implicit

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sender let's run great it passed as well

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now let's add a test unit for the

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decrement message like the previous one

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but we will send a decrement message and

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also expect no message let's run

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great now let's add a test forget count

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but we will use an implicit sender and

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send the getcount message only to make

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sure our actor starts with zero on the

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count variable so let's add an instance

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of the counter send the get count

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message and expect we will receive the

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message containing zero let's run

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excellent now let's add another test

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where we will send the increment

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decrement and get count messages let's

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create an instance of the counter then

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send to increment messages send a

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decrement message and also send another

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increment message now the counter actor

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should contain account that equals 2 so

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let's send a get count message and

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expect to receive a message that

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contains two let's run

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excellent all tests passed at the end of

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this video we implement a different unit

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test for each counter actor we use the

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recommended style from Acker you can

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check the test documentation from here

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and you'll find another style for

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testing called synchronous testing which

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uses test active ref but it's

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potentially exposed for race conditions

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and should not be used