Add tests

jest.config.js

+module.exports = {
+  // roots: ['<rootDir>/src/scripts'],
+  transform: {
+    "^.+\\.(ts|tsx)$": "ts-jest",
+  },
+  testRegex: "/tests/.*\\.(test|spec)\\.(jsx?|tsx?|ts)$",
+  moduleFileExtensions: ["ts", "tsx", "js", "jsx", "json", "node"],
+};
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tests/linear-gene.test.ts

+import linearGene from "../src/scripts/layout/linear-gene";
+import { scaleLinear } from "d3-scale";
+import { GeneData } from "../src/scripts/types";
+
+
+describe("Test linear gene layout", () => {
+  const data: GeneData[] = [{
+    name: "gene 1",
+    strand: "-",
+    begin: 10,
+    end: 50,
+    gene: "insA",
+  },
+  {
+    name: "gene 2",
+    strand: "+",
+    begin: 60,
+    end: 100,
+    gene: "yaaY",
+  }];
+  const xScale = scaleLinear()
+    .domain([0, 120])
+    .range([0, 1200])
+  const linearGeneWithPostion = linearGene(data, xScale);
+  describe("Test gene 1", () => {
+    const { position: { x, width } } = linearGeneWithPostion[0]
+    test("Test x position", () => {
+      expect(x).toBe(100);
+    });
+    test("Test width", () => {
+      expect(width).toBe(400);
+    })
+  });
+  describe("Test gene 2", () => {
+    const { position: { x, width } } = linearGeneWithPostion[1]
+    test("Test x position", () => {
+      expect(x).toBe(600);
+    })
+    test("Test width", () => {
+      expect(width).toBe(400);
+    })
+  });
+});
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