public void testMappingAnd_regular() {
    double x1 = 1.2;
    double y1 = 3.4;
    double xDelta = 5.6;
    double yDelta = 7.8;
    LinearTransformation transformation =
        LinearTransformation.mapping(x1, y1).and(x1 + xDelta, y1 + yDelta);
    assertDiagonalLinearTransformation(transformation, x1, y1, xDelta, yDelta);
  }

  public void testMappingAnd_horizontal() {
    double x1 = 1.2;

  public void testMappingAnd_regular() {
    double x1 = 1.2;
    double y1 = 3.4;
    double xDelta = 5.6;
    double yDelta = 7.8;
    LinearTransformation transformation =
        LinearTransformation.mapping(x1, y1).and(x1 + xDelta, y1 + yDelta);
    assertDiagonalLinearTransformation(transformation, x1, y1, xDelta, yDelta);
  }

  public void testMappingAnd_horizontal() {
    double x1 = 1.2;

   *
   * @since 20.0
   */
  public static final class LinearTransformationBuilder {

    private final double x1;
    private final double y1;

    private LinearTransformationBuilder(double x1, double y1) {
      this.x1 = x1;
      this.y1 = y1;
    }

    /**
     * Finish building an instance which also maps {@code x = x2} to {@code y = y2}. These values

    assertThat(transformation.transform(x1)).isWithin(ALLOWED_ERROR).of(y1);
    assertThat(transformation.transform(x1 + xDelta)).isWithin(ALLOWED_ERROR).of(y1 + yDelta);
    assertThat(transformation.inverse().transform(y1)).isWithin(ALLOWED_ERROR).of(x1);
    assertThat(transformation.inverse().transform(y1 + yDelta))
        .isWithin(ALLOWED_ERROR)
        .of(x1 + xDelta);

    assertThat(transformation.transform(x1)).isWithin(ALLOWED_ERROR).of(y1);
    assertThat(transformation.transform(x1 + xDelta)).isWithin(ALLOWED_ERROR).of(y1 + yDelta);
    assertThat(transformation.inverse().transform(y1)).isWithin(ALLOWED_ERROR).of(x1);
    assertThat(transformation.inverse().transform(y1 + yDelta))
        .isWithin(ALLOWED_ERROR)
        .of(x1 + xDelta);

    /*
     * For an explanation of the basic principle behind this check, see
     * https://stackoverflow.com/a/35754308/28465
     *
     * In that explanation's notation, our `overlap` check would be `x1 < y2 && y1 < x2`. We've
     * flipped one part of the check so that we're using "less than" in both cases (rather than a
     * mix of "less than" and "greater than"). We've also switched to "strictly less than" rather