When writing test for state machines, I came across a need for a helper that would all call flow into a path some percentage% of times.
Eg:
func TestSelfDrivingCar_BasicRun(t *testing.T) {
car := NewMockCar(t)
car.Start()
if (/* 50% probability that this will happen */) {
car.SimulateLidarFailure()
} else if /* 25% probability that this will happen */ {
car.SimulateVisionFailure()
} else {
/* 25% probability that this will happen*/
car.SimulateGearBoxFailure()
}
car.VerifySafeTrajectory()
}
You can write a small Go helper like this:
package testutils
import (
"math/rand"
"time"
)
// Odds returns True to pct% number of Check() calls
type Odds interface {
Check() bool
}
// odds returns `true` pct% of times
type odds struct {
randgen *rand.Rand
pct int
}
// NewOdds returns a odds instance with the given percent vaule
func NewOdds(pct int) Odds {
src := rand.NewSource(time.Now().UnixNano())
return &odds{
randgen: rand.New(src),
pct: pct,
}
}
// Check returns True to pct% of Check() calls
func (o *odds) Check() bool {
return o.randgen.Intn(100) < o.pct
}
Usage:
func TestSelfDrivingCar_BasicRun(t *testing.T) {
odds50pct, odds25pct := NewOdds(50), NewOdds(25)
car := NewMockCar(t)
car.Start()
if odds50pct.Check() {
car.SimulateLidarFailure()
} else if odds25pct.Check() {
car.SimulateVisionFailure()
} else {
/* 25% probability that this will happen*/
car.SimulateGearBoxFailure()
}
car.VerifySafeTrajectory()
}
ps: No, I don’t work on self-driving cars – this is just a code sample 🙂
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