func TestIsPrime(t *testing.T) {
// Check a few simple cases
cases := []struct {
n int
want bool
}{
{-1, false},
{0, false},
{1, false},
{2, true},
{3, true},
{6, false},
{1000003, true},
{1000037, true},
}
for _, c := range cases {
p := primes.IsPrime(c.n)
if p != c.want {
t.Errorf("IsPrime(%d) == %v, want %v", c.n, p, c.want)
}
}
// Check against each continguous sequence of primes that the primes
// are classified as primes and the numbers in between as not.
contiguousPrimes := [][]int{
{2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47},
{127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181},
{877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953},
{2089, 2099, 2111, 2113, 2129, 2131, 2137, 2141, 2143, 2153},
{9857, 9859, 9871, 9883, 9887, 9901, 9907, 9923, 9929, 9931},
{1000003, 1000033, 1000037},
}
for _, ps := range contiguousPrimes {
for _, p := range ps {
if !primes.IsPrime(p) {
t.Errorf("IsPrime(%d) == false, want true", p)
}
}
for i := 1; i < len(ps); i++ {
for n := ps[i-1] + 1; n < ps[i]; n++ {
if primes.IsPrime(n) {
t.Errorf("IsPrime(%d) == true, want false", n)
}
}
}
}
// Check that the numbers obtain by multiplying any two of the following
// prime factors are classified as not primes
factors := []int{2, 3, 41, 157, 953, 2141, 9929}
for i, p := range factors {
for j := 0; j <= i; j++ {
q := factors[j]
n := p * q
if primes.IsPrime(n) {
t.Errorf("IsPrime(%d) == true, want false", n)
}
}
}
}
func TestIsPrimeAgainstBaseline(t *testing.T) {
for n := -1; n < 1000; n++ {
p := primes.IsPrime(n)
q := baselineIsPrime(n)
if p != q {
t.Errorf("IsPrimeAgainstBaseline(%d) == %v, want %v", n, p, q)
}
}
for i := 0; i < 10000; i++ {
n := rand.Intn(math.MaxInt32)
p := primes.IsPrime(n)
q := baselineIsPrime(n)
if p != q {
t.Errorf("IsPrimeAgainstBaseline(%d) == %v, want %v", n, p, q)
}
}
}
func ExampleIsPrime() {
// Check which numbers are prime
ns := []int{2, 23, 49, 73, 98765, 1000003, 10007 * 10009, math.MaxInt32}
for _, n := range ns {
if primes.IsPrime(n) {
fmt.Printf("%d is prime\n", n)
} else {
fmt.Printf("%d is composite\n", n)
}
}
// Output:
// 2 is prime
// 23 is prime
// 49 is composite
// 73 is prime
// 98765 is composite
// 1000003 is prime
// 100160063 is composite
// 2147483647 is prime
}