The size of the test object can be established in different ways. The term Test Object Size Meter (TOSM) is used to indicate the size of a test object in a uniform manner. Based on a test object size determined this way, the following number can be used to estimate the functional test even without the strategy being known (yet).

1.5 to 4 hours per size unit (TOSM).

The actual number for a specific area of application depends on:

• type of environment (web, database)
• support provided
• quality of the test basis
• size of the project, towards factor 2 for very small and very big projects
• required reporting
• experience of testers.

Organisations can maintain experience figures to make ever more reliable estimates.

The size of a test object (and therefore the number of TOSMs) can be established in the following ways:

• Detailed functional description - A function point analysis can be performed on a detailed functional description (e.g. a functional design). The result of the function point analysis is a number of function points (FP). One function point is then equalled to one TOSM, making the size of the test object (= number of TOSMs) the same as the number of function points.
• Data model - If a data model is available, the following approach can be used to establish the size of the test object: determine the number of logical data collections (LDCs) and estimate the complexity. The size of the test object is found by multiplying the number of data collections by the value in the table below.

• Requirement pages - The literature contains experience figures to relate the size of the test object to the number of requirement pages. Generally speaking, this means that not all information concerning the conditions under which the data were measured is available.
• 1 A4-sized page of requirements without diagrams = 15 TOSMs [Collard, 1999].
• In a large classical project in which a highly detailed functional design without illustrations was available, the following experience figure was measured: 1 A4-sized page of requirements = 2.5 to 3 TOSMs.
• Number of screens - If the number of screens is a determinant for the size of the application, the following derivation can be used [Collard, 1999]: 1 screen (window/webpage) = 8 TOSMs.
• Program source code - For a new development project, clearly the program source code is not available until after the realisation process. For a migration or maintenance project, for instance, the derivations below may be applicable:
  • 1 kilo lines of code (3 GL) = 17 TOSMs [Collard, 1999].
  • [Jones, 1996]