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CTFL 5.1.4: Use estimation techniques to calculate the required test effort

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Syllabus section 5.1.4

5 original PrepBench practice questions for learning objective 5.1.4 of the CTFL 4.0 syllabus. Try the examples below and check each answer against its syllabus reference.

Practice questions

Question 1

Using three-point estimation, the most optimistic test effort estimate is 4 person-days, the most likely is 10 person-days, and the most pessimistic is 22 person-days. What is the final estimate E = (a + 4m + b) / 6?

  1. 10 person-days
  2. 11 person-days
  3. 12 person-days
  4. 13 person-days
Show answer
  • 10 person-days10 is the most-likely value alone; the formula weights but does not equal it.
  • Correct answer: 11 person-days(4 + 4×10 + 22) / 6 = 66 / 6 = 11 person-days.
  • 12 person-days12 overstates the result; the correct weighted average is 66 / 6 = 11.
  • 13 person-days13 does not match (4 + 40 + 22) / 6 = 11.

E = (a + 4m + b) / 6 = (4 + 4×10 + 22) / 6 = (4 + 40 + 22) / 6 = 66 / 6 = 11 person-days. Three-point estimation weights the most likely estimate four times as heavily as the extremes.

Syllabus section 5.1.4

Question 2

At this organization the development-to-test effort ratio taken from historical data is 5:2. The development effort for the next release is estimated at 900 person-days. Using estimation based on ratios, what is the estimated test effort?

  1. 180 person-days
  2. 225 person-days
  3. 300 person-days
  4. 360 person-days
Show answer
  • 180 person-days180 is one fifth of the development effort, using only the first term of the ratio.
  • 225 person-days225 is a quarter of the development effort, which the ratio does not give.
  • 300 person-days300 is a third of the development effort, which the ratio does not give.
  • Correct answer: 360 person-daysTwo fifths of 900 person-days is 360 person-days.

In estimation based on ratios, figures collected from previous projects within the organization give standard ratios that are then applied to the new project. A development-to-test ratio of 5:2 means the test effort is two fifths of the development effort, so 900 person-days of development gives 900 x 2 / 5 = 360 person-days of testing.

Syllabus section 5.1.4

Question 3

A team has finished testing 20% of a system's modules, which took 6 person-days. The modules are of similar size and complexity. Using extrapolation, what is the estimated effort to test the entire system?

  1. 12 person-days
  2. 24 person-days
  3. 30 person-days
  4. 120 person-days
Show answer
  • 12 person-days12 person-days would cover only 40% of the system, not all of it.
  • 24 person-days24 is the remaining effort after the first 20%, not the total for the whole system.
  • Correct answer: 30 person-days6 person-days for 20% extrapolates to 6 / 0.2 = 30 person-days for 100%.
  • 120 person-days120 multiplies by the wrong factor; 6 / 0.2 gives 30, not 120.

Extrapolation measures effort spent on an early portion of the work and projects it onto the whole: 6 person-days for 20% implies 6 / 0.2 = 30 person-days for 100% (of which 24 remain).

Syllabus section 5.1.4

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