Test

Go compiler ignores any file that ends its filename with _test.go.

To test math.go, create a sibling file names math_test.go.

package math

import "testing"

type testpair struct {
  values []float64
  average float64
}

var tests = []testpair{
  { []float64{1,2}, 1.5 },
  { []float64{1,1,1,1,1,1}, 1 },
  { []float64{-1,1}, 0 },
}

func TestAverage(t *testing.T) {
  for _, pair := range tests {
    v := Average(pair.values)
    if v != pair.average {
      t.Error(
        "For", pair.values,
        "expected", pair.average,
        "got", v,
      )
    }
  }
}

Run with go test in the directory.