The two ways to automate this process are to use Flow Builder and Apex trigger. Flow Builder is a tool that allows the developer to create declarative workflows that can perform logic, manipulate data, and interact with the Salesforce database. The developer can use Flow Builder to create a record-triggered flow that runs when a contact is inserted, and set the default information on the contact from the custom metadata records based on the contact's address information. The developer can also use Flow Builder to create a before-delete flow that runs when a user attempts to delete a contact, and display an error message if the contact belongs to a flagged region. Apex trigger is a code-based solution that allows the developer to execute Apex logic when a record is inserted, updated, deleted, or undeleted. The developer can use Apex trigger to create an after-insert trigger on Contact that queries the custom metadata records and sets the default information on the contact from the matching record based on the contact's address information. The developer can also use Apex trigger to create a before-delete trigger on Contact that queries the custom metadata records and throws an exception if the contact belongs to a flagged region. Remote action is not a valid answer, as it is a method that allows the developer to invoke an Apex controller method from a Visualforce page using JavaScript, but it does not automate the process. Apex invocable method is not a valid answer, as it is a method that allows the developer to expose an Apex method to a process, such as a flow or a process builder, but it does not automate the process by itself. Reference: [Flow Builder], [Apex Triggers], [Apex Developer Guide]

The reason why two Account Plan records are created whenever the Account is marked as a Customer is that the flow is configured to evaluate when a record is created and every time it is edited. This means that the flow will run both when the Account is inserted and when the Account is updated by the Apex trigger. Since the flow and the trigger both create an Account Plan record, this results in two Account Plan records being created for the same Account. To avoid this, the flow should be configured to evaluate only when a record is created or only when specified changes are made to the record. This way, the flow and the trigger will not conflict with each other and only one Account Plan record will be created . Reference: [Record-Triggered Flows], [Configure When a Record-Triggered Flow Runs]

The solution to generate the code coverage is to call the Apex class method from a test method instead of the testSetup method. The testSetup method is used to create test data that is available to all test methods in the test class, but it does not contribute to the code coverage. The test methods are used to invoke the Apex class methods and verify the results using assertions, and they do contribute to the code coverage. The developer should move the call to the Apex class method from the testSetup method to a test method, and use the System.runAs() method to run the test as a specific user, if needed. Using System.assert() in testSetup to verify the values are being returned will not help, as it will only check the expected values, but it will not generate the code coverage. Verifying the user has permissions passing a user into System.runAs() will not help, as it will only run the test as a specific user, but it will not generate the code coverage. Adding @testVisible to the method in the class the developer is testing will not help, as it will only make the method accessible to the test class, but it will not generate the code coverage. Reference: [Using the testSetup Method], [Testing Apex], [Apex Developer Guide]

A "Maximum trigger depth exceeded" error occurs when a trigger invokes itself recursively, either directly or indirectly, and exceeds the maximum stack depth. To fix this error, you can use a helper class to set a Boolean flag to TRUE the first time a trigger is fired, and then modify the trigger to only fire when the Boolean flag is FALSE. This way, you can prevent the trigger from running more than once for the same record. Splitting the trigger logic into two separate triggers does not solve the problem, as the triggers may still invoke each other recursively. Converting the trigger to use the @future annotation does not guarantee that the error will not occur, as the future method may still invoke the trigger again. The @MultiThread=true annotation does not exist in Apex. Reference: [Trigger Frameworks and Apex Trigger Best Practices], [@future Annotation]

To fix the assertion failure in the test method, a developer should add Test.startTest() before and Test.stopTest() after AuditUtil.incrementViewed(). This way, the test method can force the asynchronous @future method to execute immediately and update the Number_of_Times_Viewed__c value before the assertion. Changing the assertion to 0 or the initialization to 1 would not test the functionality of the @future method. Inserting the Account before or after the @future method would not affect the execution of the asynchronous code. Reference: [Testing Asynchronous Apex], [Test Class]