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Code coverage tools can evaluate the completeness of a test suite that was
created with any method, including black-box testing. This allows the software
team to examine parts of a system that are rarely tested and ensures that the
most important function points have been tested. Code coverage as a software
metric can be reported as a percentage for:
Function coverage, which reports on functions executed
Statement coverage, which reports on the number of lines executed to complete
the test
100% statement coverage ensures that all code paths, or branches (in terms of
control flow) are executed at least once. This is helpful in ensuring correct
functionality, but not sufficient since the same code may process different inputs
correctly or incorrectly.
Black-box testing
Black-box testing treats the software as a "black box", examining functionality
without any knowledge of internal implementation. The tester is only aware of
what the software is supposed to do, not how it does it. Black-box testing
methods include: equivalence partitioning, boundary value analysis, all-pairs
testing, state transition tables, decision table testing, fuzz testing, model-based
testing, use case testing, exploratory testing and specification-based testing.
Specification-based testing aims to test the functionality of software according to
the applicable requirements. This level of testing usually requires thorough test
cases to be provided to the tester, who then can simply verify that for a given
input, the output value (or behaviour), either "is" or "is not" the same as the
expected value specified in the test case. Test cases are built around
specifications and requirements, i.e., what the application is supposed to do. It
uses external descriptions of the software, including specifications, requirements,
and designs to derive test cases. These tests can be functional or non-functional,
though usually functional.
Specification-based testing may be necessary to assure correct functionality, but it
is insufficient to guard against complex or high-risk situations.
One advantage of the black box technique is that no programming knowledge is
required. Whatever biases the programmers may have had, the tester likely has a
different set and may emphasize different areas of functionality. On the other
hand, black-box testing has been said to be "like a walk in a dark labyrinth
without a flashlight." Because they do not examine the source code, there are
situations when a tester writes many test cases to check something that could
have been tested by only one test case, or leaves some parts of the program
untested.
This method of test can be applied to all levels of software testing: unit,
integration, system and acceptance. It typically comprises most if not all testing
at higher levels, but can also dominate unit testing as well.