test: add unit tests

example/inherited/tsconfig.base.json

@@ -0,0 +1,7 @@
+{
+  "compilerOptions": {
+    "paths": {
+      "@": []
+    }
+  }
+}

example/inherited/tsconfig.json

@@ -0,0 +1,3 @@
+{
+  "extends": "./tsconfig.preset.json"
+}

example/inherited/tsconfig.preset.json

@@ -0,0 +1,3 @@
+{
+  "extends": "./tsconfig.base.json"
+}

src/__tests__/tsconfig-loader.test.ts

@@ -3,7 +3,7 @@ import {
   tsConfigLoader,
   walkForTsConfig,
 } from "../tsconfig-loader";
-import { join } from "path";
+import { join, resolve } from "path";
 
 describe("tsconfig-loader", () => {
   it("should find tsconfig in cwd", () => {
@@ -166,3 +166,19 @@ describe("walkForTsConfig", () => {
     expect(res).toBeUndefined();
   });
 });
+
+describe("loadSyncDefault", () => {
+  it("should result multiple levels of tsconfig extension", () => {
+    const cwd = resolve(__dirname, "../../example/inherited");
+    const result = tsConfigLoader({
+      cwd,
+      getEnv: (_: string) => undefined,
+    });
+
+    expect(result).toEqual({
+      baseUrl: undefined,
+      paths: { "@": [] },
+      tsConfigPath: resolve(cwd, "tsconfig.json"),
+    });
+  });
+});

src/tsconfig-loader.ts

@@ -32,7 +32,7 @@ export function tsConfigLoader({
   return loadResult;
 }
 
-function loadSyncDefault(
+export function loadSyncDefault(
   cwd: string,
   filename?: string,
   baseUrl?: string