code: func ResolverFixed(factories map[string]Factory) Resolver {
  	return ResolverFunc(func(reqd discovery.PluginRequirements) (map[string]Factory, []error) {
  		ret := make(map[string]Factory, len(reqd))
  		var errs []error
  		for name := range reqd {
  			if factory, exists := factories[name]; exists {
  				ret[name] = factory
  			} else {
  				errs = append(errs, fmt.Errorf("provider %q is not available", name))
  			}
  		}
  		return ret, errs
  	})
  }
docs: // ResolverFixed returns a Resolver that has a fixed set of provider factories
  // provided by the caller. The returned resolver ignores version constraints
  // entirely and just returns the given factory for each requested provider
  // name.
  //
  // This function is primarily used in tests, to provide mock providers or
  // in-process providers under test.