}{},
		},
	} {
		modePairs := tc.modePairs
		if len(modePairs) == 0 {
			// Default is all modes to all modes.
			modePairs = []modePair{}
			for _, encMode := range allEncModes {
				for _, decMode := range allDecModes {
					modePairs = append(modePairs, modePair{enc: encMode, dec: decMode})
				}
			}
		}

		for _, modePair := range modePairs {
			encModeName, ok := encModeNames[modePair.enc]