Test documentation is the vital element which raises any "try out" or "experimental" activities to the level of a proper test. Even if the way something is tested is good, it is worthless if it is not documented.
How test documentation should look like is e.g. specified in the IEEE Standard 829. The IEEE standard allows scaling the set of documents by a certain degree. But basically this standard boils down to:
The scope of the test activities, the methods and tools, the schedule and sequence of all test activities related to the SW have to be stated and defined in this plan. The test objects have to be identified as well as the attributes which have to be tested and the related end of test criteria must be fixed. Responsibilities and risks have to be identified and documented.
Test design specification
The method and approach for the tests has to be defined. In some cases it may be necessary to design a sophisticated test environment (test stubs, make files, recording facilities, etc.). All the technical details have to be specified, designed and documented.
Test case specification / Test procedure specification
In the test case specification the test object has to be identified as well as the attributes which have to be tested. It has to be made clear which steps and measures have to be applied to execute the test cases and which results are expected.
Test log / Test recording / Test reporting
The test results have to be documented and it has to be identified if the test ended with the expected results i.e. if they passed or failed. The test recording strongly depends on the test environment. In some cases this can be an automatic printout. In other cases this may be a check list which is ticked by the tester (may be even included in the test procedure / test case specification!). It may be even necessary to apply different methods within the same project, depending on the kind of test object and the kind of test employed. A preparation of the test results in a report is required. Test logs may be voluminous and have to be condensed to have their contents prepared for a quick overview and reference as well as for management or customer presentations.