message: only enable run this command if the command is valid
diff: @@ -18,6 +18,7 @@ export default class ToolBar extends React.Component {
  const isPlayingSuite = PlaybackState.isPlaying && PlaybackState.currentRunningSuite;
  const isPlayingTest = PlaybackState.isPlaying && PlaybackState.currentRunningTest && !PlaybackState.currentRunningSuite;
  const isTestEmpty = UiState.selectedTest.test && !UiState.selectedTest.test.commands.length;
  + const isCommandValid = UiState.selectedCommand && UiState.selectedCommand.isValid;
  return (
  <div className="toolbar">
  <PlayAll
  @@ -35,7 +36,7 @@ export default class ToolBar extends React.Component {
  <Pause isActive={PlaybackState.paused}
  data-tip={!PlaybackState.paused ? "<p>Pause test execution</p>" : "<p>Resume test execution</p>"}
  onClick={!PlaybackState.paused ? PlaybackState.pause : PlaybackState.resume} /> : null }
  - { !PlaybackState.isPlaying ? <StepInto disabled={!UiState.selectedCommand} onClick={() => PlaybackState.playCommand(UiState.selectedCommand)} /> : null }
  + { !PlaybackState.isPlaying ? <StepInto disabled={!isCommandValid} onClick={() => PlaybackState.playCommand(UiState.selectedCommand)} /> : null }
  <GaugeMenu opener={
  <SpeedGauge speed={UiState.gaugeSpeed} />
  } value={PlaybackState.delay} maxDelay={PlaybackState.maxDelay} onChange={PlaybackState.setDelay} />
  