public abstract boolean isVertical();

  /** Returns whether this is a horizontal transformation. */
  public abstract boolean isHorizontal();

  /**
   * Returns the slope of the transformation, i.e. the rate of change of {@code y} with respect to
   * {@code x}. This must not be called on a vertical transformation (i.e. when {@link
   * #isVertical()} is true).
   */
  public abstract double slope();

}\n\n  const placement = data.placement.split('-')[0];\n  const { popper, reference } = data.offsets;\n  const isVertical = ['left', 'right'].indexOf(placement) !== -1;\n\n  const len = isVertical ? 'height' : 'width';\n  const sideCapitalized = isVertical ? 'Top' : 'Left';\n  const side = sideCapitalized.toLowerCase();\n  const altSide = isVertical ? 'left' : 'top';\n  const opSide = isVertical ? 'bottom' : 'right';\n  const arrowElementSize = getOuterSizes(arrowElement)[len];\n\n  //\n  // extends keepTogether...

    double x1 = 1.2;
    double y1 = 3.4;
    double slope = Double.MIN_VALUE;
    LinearTransformation transformation = LinearTransformation.mapping(x1, y1).withSlope(slope);
    assertThat(transformation.isVertical()).isFalse();
    assertThat(transformation.isHorizontal()).isFalse();
    assertThat(transformation.slope()).isWithin(ALLOWED_ERROR).of(slope);

    double x1 = 1.2;
    double y1 = 3.4;
    double slope = Double.MIN_VALUE;
    LinearTransformation transformation = LinearTransformation.mapping(x1, y1).withSlope(slope);
    assertThat(transformation.isVertical()).isFalse();
    assertThat(transformation.isHorizontal()).isFalse();
    assertThat(transformation.slope()).isWithin(ALLOWED_ERROR).of(slope);