To determine the minimum set of test input values to cover all valid equivalence partitions, we need to consider the different temperature ranges and conditions mentioned in the question.

Based on the information given, we can identify the following equivalence partitions:

1. Below 18 degrees (heating switched on)
2. Between 18 and 21 degrees (heating switched off)
3. Above 21 degrees (heating switched off)

To cover all valid equivalence partitions, we need to select test input values that represent each partition.

Let's analyze each option to see if it covers all the partitions:

Option A: 15, 19, 25

• 15 is below 18 degrees (heating switched on)
• 19 is between 18 and 21 degrees (heating switched off)
• 25 is above 21 degrees (heating switched off)

Option B: 17, 18, 20, 21

• 17 is below 18 degrees (heating switched on)
• 18 is between 18 and 21 degrees (heating switched off)
• 20 is between 18 and 21 degrees (heating switched off)
• 21 is above 21 degrees (heating switched off)

Option C: 18, 20, 22

• 18 is between 18 and 21 degrees (heating switched off)
• 20 is between 18 and 21 degrees (heating switched off)
• 22 is above 21 degrees (heating switched off)

Option D: 16, 26

• 16 is below 18 degrees (heating switched on)
• 26 is above 21 degrees (heating switched off)

Based on the analysis, Option A covers all the valid equivalence partitions. It includes a temperature below 18 degrees (heating switched on), a temperature between 18 and 21 degrees (heating switched off), and a temperature above 21 degrees (heating switched off).

Therefore, the correct answer is Option A: 15, 19, 25.

• Thanks
• Wrong explanation