code: function LinkPO(index) {
      this.index = index;
  
      this.getLine = () => cy.get('path[class="link"]').then(lines => lines[this.index]);
      this.getStyle = () => this.getLine().invoke("attr", "style");
      this.shouldHaveColor = color => this.getStyle().should("contain", `stroke: ${color};`);
      this.shouldHaveOpacity = opacity => this.getStyle().should("contain", `opacity: ${opacity};`);
      this.hasMarker = () =>
          this.getLine()
              .invoke("attr", "marker-end")
              .should("contain", "url(#marker-");
      this.getLabel = () => this.getLine().siblings();
  }
docs: Page Object for interacting with Link component.
  @param {number} index - the index of the link.
  @returns {undefined}