Unit test for sending emails in Apex

TestEmailSend.cls

@isTest
public class TestEmailSend {
    @isTest
    static void testTheEmail(){
        Test.startTest();
            // the method we're testing
            // https://gist.github.com/techb/7519e95bac3caa2b8adb3f65d2dc2dc8
            EmailSend.sendEmail('test@test.com');
        
            // we assert buy what govener limits say 
            Integer invocations = Limits.getEmailInvocations();
        Test.stopTest();
        System.assertEquals(1, invocations, 'Email has not been sent');
    }
}