1. Cases for operations
1.1. when result = 0
1.2. result > 0
1.3. result < 0
1.4. Empty string +-/* int/float
1.5. Borders
1.5.1. Max positive result
1.5.2. Max positive result -1
1.5.3. Max positive result + 1
1.5.4. Max negative result
1.5.5. Max negative result -1
1.5.6. Max negative result + 1
2. Addition
2.1. int + int
2.1.1. Positive + Positive
2.1.2. negative + negative
2.1.3. positive + negative
2.2. int+ float
2.2.1. Positive + Positive
2.2.2. negative + negative
2.2.3. positive + negative
2.3. float + float
2.3.1. Positive + Positive
2.3.2. negative + negative
2.3.3. positive + negative
3. Square
3.1. Int
3.1.1. positive
3.1.2. negative
3.2. float
3.2.1. positive
3.2.2. negative
3.3. null
3.4. empty string
4. Square root
4.1. int
4.1.1. positive
4.1.2. negative
4.2. float
4.2.1. positive
4.2.2. negative
4.3. null
4.4. empty string
5. M+/M-
5.1. Int
5.1.1. Positive
5.1.2. negative
5.2. null
5.3. Float
5.3.1. Positive
5.3.2. Negative
5.4. Error handling when result bigger/lower than maximum/minimum possible value
6. Сonstituent components
6.1. Screen
6.1.1. Resolution
6.1.2. Height/Width
6.1.3. Safety
6.1.4. Use during different weather condition
6.1.5. Material
6.1.6. Quality
6.1.7. How much characters can represent?
6.2. Buttons
6.2.1. Meterial
6.2.2. Size
6.2.3. Location
6.2.4. Grouping
6.2.5. Color
6.2.6. Shape
6.2.7. Usability
6.2.8. Safety
6.2.9. Marked?
6.2.10. Pressure
6.3. Outer part
6.3.1. Material
6.3.2. Size
6.3.3. Weight
6.3.4. Safety
6.3.5. Usabilty
6.3.6. Color
6.3.7. Quality
6.4. Battery
6.4.1. Type
6.4.2. Safety
6.4.3. Charge time
6.4.4. Need a charge?
6.4.4.1. How long it takes to charge?
6.4.5. How long can work?
6.4.6. Will automatically switch off if user inactive?
7. Clear
7.1. Does it delete character by character?
8. Subtraction
8.1. Integer - Integer
8.1.1. Positive - Positive
8.1.2. negative - negative
8.1.3. positive - negative
8.1.4. negative - positive
8.2. Integer - float
8.2.1. Positive - Positive
8.2.2. negative - negative
8.2.3. positive - negative
8.2.4. negative - positive
8.3. float - int
8.3.1. Positive - Positive
8.3.2. negative - negative
8.3.3. positive - negative
8.3.4. negative - positive
9. Division
9.1. int / int
9.1.1. Positive / Positive
9.1.2. negative / negative
9.1.3. positive /negative
9.2. int / float
9.2.1. Positive / Positive
9.2.2. negative / negative
9.2.3. positive /negative
9.3. int / 0
9.3.1. Positive / 0
9.3.2. negative / 0
9.4. float / 0
9.4.1. Positive / 0
9.4.2. negative / 0
9.5. 0 / int
9.5.1. 0 /positive
9.5.2. 0 / negative
9.6. 0 / float
9.6.1. 0 /positive
9.6.2. 0 / negative
10. Multiplying
10.1. int * int
10.1.1. Positive * Positive
10.1.2. negative * negative
10.1.3. positive * negative
10.2. Int * float
10.2.1. negative * negative
10.2.2. Positive * Positive
10.2.3. positive * negative
10.3. Int * 0
10.3.1. positive * 0
10.3.2. negative * 0
10.4. Float * 0
10.4.1. negative * 0
10.4.2. positive * 0
11. Data types
11.1. Float
11.1.1. Positive
11.1.1.1. lowest
11.1.1.2. Highest
11.1.1.3. Highest + 1
11.1.1.4. highest - 1
11.1.1.5. lowest +1
11.1.1.6. Lowest - 1
11.1.2. Negative
11.1.2.1. lowest
11.1.2.2. Highest
11.1.2.3. Highest + 1
11.1.2.4. highest - 1
11.1.2.5. lowest +1
11.1.2.6. Lowest - 1
11.1.3. With 2 dots?
11.2. Integer
11.2.1. Positive
11.2.1.1. lowest
11.2.1.2. Highest
11.2.1.3. Highest + 1
11.2.1.4. highest - 1
11.2.1.5. lowest +1
11.2.1.6. Lowest - 1
11.2.2. Negative
11.2.2.1. lowest
11.2.2.2. Highest
11.2.2.3. Highest + 1
11.2.2.4. highest - 1
11.2.2.5. lowest +1
11.2.2.6. Lowest - 1
11.3. Null
12. Clear all
12.1. Does it clear all data for all operations?
13. Memory
13.1. Does it work for all operations?
13.2. Does it work after calculator was switched off and switched on?
13.2.1. Automatically
13.2.2. By user