Add unit tests for body seralization

src/__test__/fetchers/body.test.ts

@@ -0,0 +1,39 @@
+import { serializeBody } from "@/fetchers/body";
+import FormData from "form-data";
+import { describe, expect, it } from "vitest";
+
+describe("serializeBody()", () => {
+  it('should work with standard text', () => {
+    expect(serializeBody("hello world")).toEqual({
+      headers: {},
+      body: "hello world"
+    })
+  })
+
+  it('should work with objects', () => {
+    expect(serializeBody({ hello: "world", a: 42 })).toEqual({
+      headers: {
+        "Content-Type": "application/json"
+      },
+      body: JSON.stringify({ hello: "world", a: 42 })
+    })
+  })
+
+  it('should work x-www-form-urlencoded', () => {
+    const obj = new URLSearchParams()
+    obj.set("a", "b");
+    expect(serializeBody(obj)).toEqual({
+      headers: {},
+      body: obj
+    })
+  })
+  
+  it('should work multipart/form-data', () => {
+    const obj = new FormData()
+    obj.append("a", "b");
+    expect(serializeBody(obj)).toEqual({
+      headers: {},
+      body: obj
+    })
+  })
+})