A project can expect to have dozens or hundreds of files testing specific features in a stand-alone way. We may wonder if there are any interactions between features that will cause any of these tests to fail. AllCombinations explores this. It is a fixture that enumerates cases by drawing one file at a time from each of a number of lists; running each in turn, and then repeating the drawing and running for all possible combinations.
For the purpose of illustration we've created a number of files that contain small tests of the CalculatorExample. We've categorized the files as magnitudes, signs and functions, which enter values, changes signs, and compute functions, respectivly.
The number of cases will as large as the product of the size of each list of tests. The searches in the table find four magnitues, three signs and two functions.
If the tests are intended to interact, as ours are here, then some care is required to be sure that checks in the tests are independent of this interaction. No checks at all my be suitable if we are only testing that there are no exceptions thrown. Or the simplest checks may be adaquate so long as features are tested well in isolation. It may be convenient to run a simulation, a so called oracale, along side the application to generate expected results.
The fixture inherits path expansion from AllFiles, but captures these by overrinding doRows(Parse, List) and saving the list of files in a list of lists. Then, at the end of doTable, the fixture gets to work computing and running combinations.