“Exploratory Testing”

Exploratory testing is an approach to software testing that is concisely described as simultaneous learning, test design and test execution. Cem Kaner, who coined the term in 1983, now defines exploratory testing as "a style of software testing that emphasizes the personal freedom and responsibility of the individual tester to continually optimize the quality of his/her work by treating test-related learning, test design, test execution, and test result interpretation as mutually supportive activities that run in parallel throughout the project.
While the software is being tested, the tester learns things that together with experience and creativity generates new good tests to run. Exploratory testing is often thought of as a black box testing technique. Instead, those who have studied it consider it a test approach that can be applied to any test technique, at any stage in the development process. The key is not the test technique nor the item being tested or reviewed; the key is the cognitive engagement of the tester, and the tester's responsibility for managing his or her time.
The essence of exploratory testing is that you learn while you test, and you design your tests based on what you are learning.
• One definition (Bach's) is “Any testing to the extent that the tester actively controls the design of the tests as those tests are performed and uses information gained while testing to design new and better tests.”
• Another definition (Bach/Kaner) is any testing process that involves simulations learning, test design, and test execution.
The examples below only scratch the surface of the exploratory process, because they show an easily-understood sequence of test / result / follow-up test / result and so on. We learn as we go, but we only learn from the results of the individual tests. In an exploratory session,
• The tester might have been following up a more carefully researched risk analysis to get to the starting point of this sequence, and thus might have a much deeper interpretation of the test results than the superficial presentation we give here
• At any point in the session, the tester might stop test execution to read, ask questions, or learn more about the program and its risks before designing and running the next test.
Any type of test can be designed and/or used in an exploratory way.
Benefits and drawbacks
The main advantage of exploratory testing is that less preparation is needed, important bugs are found quickly, and at execution time, the approach tends to be more intellectually stimulating than execution of scripted tests.
Another major benefit is that testers can use deductive reasoning based on the results of previous results to guide their future testing on the fly. They do not have to complete a current series of scripted tests before focusing in on or moving on to exploring a more target rich environment. This also accelerates bug detection when used intelligently.
Another benefit is that, after initial testing, most bugs are discovered by some sort of exploratory testing. This can be demonstrated logically by stating, "Programs that pass certain tests tend to continue to pass the same tests and are more likely to fail other tests or scenarios that are yet to be explored."
Disadvantages
Disadvantages are that tests invented and performed on the fly can't be reviewed in advance (and by that prevent errors in code and test cases), and that it can be difficult to show exactly which tests have been run.
Freestyle exploratory test ideas, when revisited, are unlikely to be performed in the exact same manner, which can be an advantage if it is important to find new errors; or a disadvantage if it is more important to repeat specific details of the earlier tests. This can be controlled with specific instruction to the tester, or by preparing automated tests where feasible, appropriate, and necessary, and ideally as close to the unit level as possible Usage
Exploratory testing is particularly suitable if requirements and specifications are incomplete, or if there is lack of time. The approach can also be used to verify that previous testing has found the most important defects. It is common to perform a combination of exploratory and scripted testing where the choice is based on risk.