Add math run and fraction

src/file/paragraph/math/math-run.spec.ts

@@ -0,0 +1,21 @@
+import { expect } from "chai";
+
+import { Formatter } from "export/formatter";
+
+import { MathRun } from "./math-run";
+
+describe("MathRun", () => {
+    describe("#constructor()", () => {
+        it("should create a MathRun with correct root key", () => {
+            const mathRun = new MathRun("2+2");
+            const tree = new Formatter().format(mathRun);
+            expect(tree).to.deep.equal({
+                "m:r": [
+                    {
+                        "m:t": ["2+2"],
+                    },
+                ],
+            });
+        });
+    });
+});