A TDD practice exercise suggested by Jason Gorman in his book on the subject - Codemanship - TDD.
Writing the assertions first and working backwards to the set-up, test-drive some code to calculate how much water will be needed to to fill the following:
- A cube
- A cylinder
- A pyramid
To calculate the volume of any solid, there are two steps required:
- Calculate the volume in cubic cm - cm3.
- Convert the volume in cm3 to litres.
The formula for calculating the volume of a cube in cm3 is L x W x H:
10cm x 10cm x 10cm = 1000cm3
1 litre is equal to 1000cm3. Therefore to calculate the volume of water needed to fill the cube in litres, you can simply divide the cm3 volume by 1000:
1000cm3 / 1000 = 1 litre.
The formula for calculating the volume of a cylinder is π x r2 x H:
π x 10cm2 x 10cm
which is also:
π x 100cm x 10cm = 3141.59cm3
Therefore the volume of this cylinder is 3141.59cm3 / 1000 = 3.14 litres
The formula for calculating the volume of a pyramid is 1/3 x L x W x H:
1/3 x 10cm3 x 10cm3 10cm3 = 333.33cm3
Therefore the volume of this pyramid is 333.33cm3 / 1000 = 0.33 litres
It would be good to separate the calculation of the area of the solid first, perhaps with a Solid interface:
interface Solid {
getAreaInCubicCentimetres(): number;
}
And then the class can implement this interface. For example a cube:
class Cube implements Solid {
#length: number;
#width: number;
#height: number;
constructor(length: number, width: number, height: number) {
this.#length = length;
this.#width = width;
this.#height = height;
}
get length(): number {
return this.#length;
}
get width(): number {
return this.#width;
}
get height(): number {
return this.#height;
}
getAreaInCubicCentimetres(): number {
return this.length * this.width * this.height;
}
}
Following this, a class called VolumeCalculator
can accept a solid class to retrieve its area:
class VolumeCalculator {
getRequiredLitresOfWater(solid: Solid): number {
return solid.getAreaInCubicCentimetres() / 1000;
}
}
const cube = new Cube(10, 10, 10);
const volumeCalculator = new VolumeCalculator();
const litres = volumeCalculator.getRequiredLitresOfWater(cube);
Something along these lines.