prow/config/tide.go
func (cp *TideContextPolicy) MissingRequiredContexts(contexts []string) []string {
	if len(cp.RequiredContexts) == 0 {
		return nil
	}
	existingContexts := sets.NewString()
	for _, c := range contexts {
		existingContexts.Insert(c)
	}
	var missingContexts []string
	for c := range sets.NewString(cp.RequiredContexts...).Difference(existingContexts) {
		missingContexts = append(missingContexts, c)
	}
	return missingContexts
}
func (cp *TideContextPolicy) MissingRequiredContexts(contexts []string) []string {
	if len(cp.RequiredContexts) == 0 {
		return nil
	}
	existingContexts := sets.NewString()
	for _, c := range contexts {
		existingContexts.Insert(c)
	}
	var missingContexts []string
	for c := range sets.NewString(cp.RequiredContexts...).Difference(existingContexts) {
		missingContexts = append(missingContexts, c)
	}
	return missingContexts
}
// MissingRequiredContexts discard the optional contexts and only look of extra required contexts that are not provided.