Testing can be classified by degree of formality:
Test case-based testing (scripted testing) is a formal approach to software testing that focuses on control and precision. Testing effort is managed by developing and reviewing all the test cases, test case suites, test scripts and other documentation. It is the most widely used testing technique which allows to achieve maximum code coverage through process systematization, usage of convenient metrics and a variety of the proven methodologies that have been employed for decades.
Scripted approach does not require a lot of testers and has the advantage of many kinds of resources to execute the tests since skillful test designers make tests scripts intelligent.
Software test outsourcing is a testing carried out by third parties so that to help businesses release high quality projects even if they are late or already developed. Regardless of a scope and complexity of the project and frequency of QA & testing needs, as well as stage of the development life cycle, an offshore testing team can do the job to a high professional standard.
Exploratory testing is a partially formal approach to testing of a software application that is contrasted to scripted testing. This process involves studying about the product while simultaneously developing and running tests. The goal is to discover and investigate the program as the end user would, likely to detect new bugs as you go. In exploratory testing, the testers have more freedom to run tests, they do not need to follow any instructions since this process is unstructured, unplanned and unfocused. However, prepared test scenarios validate the quality of the software. There is also a scenario-based approach, used by providers of exploratory testing services. It is also called session-based testing that tends to combine exploratory and accountability testing techniques to ensure fast bug discovery; it provides metrics for the progress measurement and execution coverage.
Ad-hoc testing is absolutely informal approach to testing process which requires neither test cases, nor test scripts or test scenarios. For this reason, it is performed only by highly qualified and experienced testers that is why it is called experience-based testing. Ad-hoc testing precedes all formal types of testing of the software. All means can be used during this testing if they are believed to help to identify defects in the application. These tests are executed only once unless a bug is detected.
Outsourcing software testing you will manage to reduce costs in terms of money, time and human resources.