How to use the viewport-mercator-project.flyToViewport function in viewport-mercator-project

interpolateProps(startProps: MapStateProps, endProps: MapStateProps, t: number) {
    const viewport = flyToViewport(startProps, endProps, t, this.props);

    // Linearly interpolate 'bearing' and 'pitch' if exist.
    for (const key of LINEARLY_INTERPOLATED_PROPS) {
      viewport[key] = lerp(startProps[key], endProps[key], t);
    }

    return viewport;
  }

.forEach(testCase => {
    const propsInTransition = flyToViewport(
      testCase.startProps, testCase.endProps, testCase.t);
    t.deepEqual(toLowPrecision(propsInTransition, 7), testCase.expect, 'interpolated correctly');
  });