Numeric types and everything else that implements IComparable<T>

int theInt = 5;
theInt.Should().BeGreaterThanOrEqualTo(5);
theInt.Should().BeGreaterThanOrEqualTo(3);
theInt.Should().BeGreaterThan(4);
theInt.Should().BeLessThanOrEqualTo(5);
theInt.Should().BeLessThan(6);
theInt.Should().BePositive();
theInt.Should().Be(5);
theInt.Should().NotBe(10);
theInt.Should().BeInRange(1, 10);
theInt.Should().NotBeInRange(6, 10);
theInt.Should().Match(x => x % 2 == 1);

theInt = 0;
//theInt.Should().BePositive(); => Expected positive value, but found 0
//theInt.Should().BeNegative(); => Expected negative value, but found 0

theInt = -8;
theInt.Should().BeNegative();
int? nullableInt = 3;
nullableInt.Should().Be(3);

double theDouble = 5.1;
theDouble.Should().BeGreaterThan(5);
byte theByte = 2;
theByte.Should().Be(2);

Notice that Should().Be() and Should().NotBe() are not available for floats and doubles. Floating point variables are inheritably inaccurate and should never be compared for equality. Instead, either use the Should().BeInRange() method or the following method specifically designed for floating point or decimal variables.

float value = 3.1415927F;
value.Should().BeApproximately(3.14F, 0.01F);

This will verify that the value of the float is between 3.13 and 3.15.

Conversely, to assert that the value differs by an amount, you can do this.

float value = 3.5F;
value.Should().NotBeApproximately(2.5F, 0.5F);

This will verify that the value of the float is not between 2.0 and 3.0.

Float and double values may take the special value NaN. To verify, you can do this.

float value = float.NaN;
value.Should().BeNaN();

This will verify that the value of the float is anything other than the special value NaN.

float value = float.NaN;
value.Should().NotBeNaN();

To assert that a value matches one of the provided values, you can do this (works for numeric types and IComparables).

value.Should().BeOneOf(new[] { 3, 6 });

On .NET 8 or later, the same assertions are also available for any other type that implements System.Numerics.INumber<T>, such as Half or NFloat. BeApproximately and NotBeApproximately work for every IFloatingPoint<T>.

Half value = (Half)1.5;
value.Should().BeApproximately((Half)1.5, (Half)0.01);