TriangleTest.cs

using System;
using System.Threading.Tasks;
using Xunit;

namespace UnitTest {
    public class Triangle {
        [Fact]
        public void CalculateArea_WithValidTriangle_ShouldReturnCorrectArea () {
            Assert.Equal (24, CalculateArea (6, 8, 10));
        }

        [Fact]
        public void CalculateArea_WithAnySidesEquallingZero_ShouldReturnException () {
            Assert.Throws<ArgumentException> (() => CalculateArea (0, 4, 5));
            Assert.Throws<ArgumentException> (() => CalculateArea (3, 0, 5));
            Assert.Throws<ArgumentException> (() => CalculateArea (3, 4, 0));
        }

        [Fact]
        public void CalculateArea_WithAnySidesLowerThanZero_ShouldReturnException () {
            Assert.Throws<ArgumentException> (() => CalculateArea (-1, 4, 5));
            Assert.Throws<ArgumentException> (() => CalculateArea (3, -1, 5));
            Assert.Throws<ArgumentException> (() => CalculateArea (3, 4, -1));
        }

        [Fact]
        public void CalculateArea_WithoutValidTriangle_ShouldReturnException () {
            Assert.Throws<ArgumentException> (() => CalculateArea (1, 4, 5));
            Assert.Throws<ArgumentException> (() => CalculateArea (10, 20, 50));
            Assert.Throws<ArgumentException> (() => CalculateArea (37, 42, 101));
        }
        
        [Fact]
        public void CalculatePerimeter_WithValidTriangle_ShouldReturnCorrectPerimeter () {
            Assert.Equal (12, CalculatePerimeter (3, 4, 5));
        }

        [Fact]
        public void CalculatePerimeter_WithAnySidesEquallingZero_ShouldReturnException () {
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (0, 4, 5));
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (3, 0, 5));
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (3, 4, 0));
        }

        [Fact]
        public void CalculatePerimeter_WithAnySidesLowerThanZero_ShouldReturnException () {
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (-1, 4, 5));
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (3, -1, 5));
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (3, 4, -1));
        }

        [Fact]
        public void CalculatePerimeter_WithoutValidTriangle_ShouldReturnException () {
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (1, 4, 5));
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (10, 20, 50));
            Assert.Throws<ArgumentException> (() => CalculatePerimeter (37, 42, 101));
        }

        double CalculateArea (int a, int b, int c) {
            if (a == 0 || b == 0 || c == 0)
                throw new ArgumentException ("Sides should not be zero");

            if (a < 0 || b < 0 || c < 0)
                throw new ArgumentException ("Sides should not be negatives");

            if (a + b <= c || a + c <= b || b + c <= a)
                throw new ArgumentException ("This is not a valid triangle");

            return (0.25 * Math.Sqrt ((a + b + c) * (-a + b + c) * (a - b + c) * (a + b - c)));
        }

        double CalculatePerimeter (int a, int b, int c) {
            if (a == 0 || b == 0 || c == 0)
                throw new ArgumentException ("Sides should not be zero");

            if (a < 0 || b < 0 || c < 0)
                throw new ArgumentException ("Sides should not be negatives");

            if (a + b <= c || a + c <= b || b + c <= a)
                throw new ArgumentException ("This is not a valid triangle");

            return a + b + c;
        }
    }
}