A ‘finally’ block is a code block that follows a try-catch structure and is executed regardless of whether an exception is thrown or caught in the try-catch blocks. Its primary purpose is to execute necessary cleanup code such as closing file streams, releasing network resources, or resetting variable states, which must occur irrespective of whether an exception was thrown or handled. The use of a ‘finally’ block is crucial in scenarios where there are operations in the try block that might not complete successfully, and yet some cleanup or final operations must be guaranteed to run. For example, if an exception occurs while reading a file, the file stream should still be closed to prevent resource leaks. A ‘finally’ block ensures such cleanup happens reliably, maintaining the integrity and efficiency of the program, especially in resource-constrained environments or where resource leaks might lead to serious application failures or security vulnerabilities.

Exception handling generally requires manual coding to effectively address the specific context and error condition of each exception. The catch blocks and the logic within them need to be thoughtfully designed to suit the particular issue they are meant to handle. However, some aspects of exception handling can be somewhat automated or made less tedious. For instance, logging frameworks can automate the process of recording exceptions and the context in which they occur. Some modern IDEs provide templates or snippets for common exception handling patterns, which can speed up the coding process. There are also programming paradigms, like aspect-oriented programming, which can centralize and somewhat automate handling of cross-cutting concerns like logging and exception handling. However, the core decision-making regarding how to handle each specific exception, whether to retry operations, prompt user for input, or fail gracefully, still predominantly relies on bespoke, manual coding to ensure the correct handling tailored to the application’s logic and user experience.

Using exceptions for control flow is considered poor practice due to several reasons. Firstly, exceptions are generally intended for exceptional, error-like conditions and using them for regular control flow disrupts the semantic clarity of the code, making it harder to understand and maintain. Exception handling typically incurs a higher computational cost compared to regular control structures like loops and conditional statements, thus impacting the performance negatively. Moreover, employing exceptions for flow control can mask real errors, as the code is structured to expect and handle exceptions as part of the normal operations. Such a setup might lead to neglecting or overlooking genuine exception conditions that indicate a flaw or an issue in the program logic. A well-designed program should use standard control structures for regular control flow and reserve exceptions for unexpected, abnormal conditions outside the usual operation of the program.

Checked and unchecked exceptions represent two primary categories of exceptions in many programming languages, like Java. Checked exceptions are those which the compiler checks at compile time. They are used for events that a programmer should anticipate and plan for, such as trying to read a file that doesn't exist (‘FileNotFoundException’). Unchecked exceptions, on the other hand, are not checked at compile time. They are mostly the runtime exceptions like ‘NullPointerException’, indicating issues due to flaws in program logic, or unforeseen circumstances like arithmetic overflow. The critical difference in handling these lies in their predictability and the nature of errors they signify. Checked exceptions must be either caught in a try-catch block or declared in the method signature, forcing the programmer to consider these potential issues during development. Unchecked exceptions, being mostly runtime anomalies, are often not explicitly handled unless the programmer anticipates a specific runtime issue that needs intervention. Understanding this distinction is vital for developing robust software, where the handling strategy depends on the exception's nature and the context in which it occurs.

Testing and ensuring the effectiveness of exception handling code involves a few strategic approaches:

1. Unit Testing: Write unit tests that specifically trigger exceptions in your code. Use a testing framework to simulate various error conditions and assert that your code handles these exceptions as expected.
2. Code Coverage Tools: Utilize code coverage tools to ensure that your exception handling code is being executed during tests. This tool helps in identifying untested paths, including exception scenarios.
3. Boundary Testing: Test edge cases and boundary conditions which are likely to produce exceptions, ensuring that your handling code correctly addresses these scenarios.
4. Integration Testing: Beyond unit tests, perform integration testing to see how different parts of your application interact and manage exceptions. This helps in uncovering any unintended side effects or propagation issues.
5. Review and Analysis: Conduct regular code reviews and static analysis to check for best practices in exception handling, such as avoiding generic catch blocks, proper resource management, and not using exceptions for control flow.
6. Performance Testing: In scenarios where exceptions might be frequent, test the performance impact of your exception handling. Exceptions should not significantly degrade the application performance under normal operation.

Effective testing of exception handling ensures that your application can handle unexpected events gracefully, maintain security, provide a positive user experience, and avoid resource leaks or failures.