diff --git a/packages/core/tests/__snapshots__/config.test.ts.snap b/packages/core/tests/__snapshots__/config.test.ts.snap
new file mode 100644
index 000000000..e7b7f55a2
--- /dev/null
+++ b/packages/core/tests/__snapshots__/config.test.ts.snap
@@ -0,0 +1,109 @@
+// Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
+
+exports[`Should compose create Rsbuild config correctly > Merge Rsbuild config 1`] = `
+[
+  {
+    "output": {
+      "distPath": {
+        "js": "./",
+      },
+      "filenameHash": false,
+      "minify": false,
+    },
+    "source": {
+      "alias": {
+        "bar": "bar",
+        "foo": "foo/esm",
+      },
+      "preEntry": "./b.js",
+    },
+    "tools": {
+      "htmlPlugin": false,
+      "rspack": {
+        "experiments": {
+          "outputModule": true,
+        },
+        "optimization": {
+          "concatenateModules": true,
+        },
+        "output": {
+          "library": {
+            "type": "module",
+          },
+          "module": true,
+        },
+      },
+    },
+  },
+  {
+    "output": {
+      "distPath": {
+        "js": "./",
+      },
+      "filenameHash": false,
+      "minify": false,
+    },
+    "source": {
+      "alias": {
+        "bar": "bar/cjs",
+        "foo": "foo",
+      },
+      "preEntry": [
+        "./a.js",
+        "./c.js",
+        "./d.js",
+      ],
+    },
+    "tools": {
+      "htmlPlugin": false,
+      "rspack": {
+        "experiments": {
+          "outputModule": true,
+        },
+        "optimization": {
+          "concatenateModules": true,
+        },
+        "output": {
+          "library": {
+            "type": "module",
+          },
+          "module": true,
+        },
+      },
+    },
+  },
+  {
+    "output": {
+      "distPath": {
+        "js": "./",
+      },
+      "filenameHash": false,
+      "minify": false,
+    },
+    "source": {
+      "alias": {
+        "bar": "bar",
+        "foo": "foo",
+      },
+      "preEntry": "./a.js",
+    },
+    "tools": {
+      "htmlPlugin": false,
+      "rspack": {
+        "experiments": {
+          "outputModule": true,
+        },
+        "optimization": {
+          "concatenateModules": true,
+        },
+        "output": {
+          "library": {
+            "type": "module",
+          },
+          "module": true,
+        },
+      },
+    },
+  },
+]
+`;
diff --git a/packages/core/tests/config.test.ts b/packages/core/tests/config.test.ts
new file mode 100644
index 000000000..3a94feebb
--- /dev/null
+++ b/packages/core/tests/config.test.ts
@@ -0,0 +1,185 @@
+import { join } from 'node:path';
+import { describe, expect, test } from 'vitest';
+import { composeCreateRsbuildConfig, loadConfig } from '../src/config';
+import type { RslibConfig } from '../src/types/config';
+
+describe('Should load config file correctly', () => {
+  test('Load config.js in cjs project', async () => {
+    const fixtureDir = join(__dirname, 'config/cjs');
+    const configDir = join(fixtureDir, 'rslib.config.js');
+    const config = await loadConfig(configDir);
+    expect(config).toEqual({
+      lib: [],
+      source: {
+        entry: {
+          main: './foo/index.js',
+        },
+      },
+      _privateMeta: {
+        configFilePath: configDir,
+      },
+    });
+  });
+
+  test('Load config.mjs in cjs project', async () => {
+    const fixtureDir = join(__dirname, 'config/cjs');
+    const configDir = join(fixtureDir, 'rslib.config.mjs');
+    const config = await loadConfig(configDir);
+    expect(config).toEqual({
+      lib: [],
+      source: {
+        entry: {
+          main: './foo/index.js',
+        },
+      },
+      _privateMeta: {
+        configFilePath: configDir,
+      },
+    });
+  });
+
+  test('Load config.ts in cjs project', async () => {
+    const fixtureDir = join(__dirname, 'config/cjs');
+    const configDir = join(fixtureDir, 'rslib.config.ts');
+    const config = await loadConfig(configDir);
+    expect(config).toEqual({
+      lib: [],
+      source: {
+        entry: {
+          main: './foo/index.ts',
+        },
+      },
+      _privateMeta: {
+        configFilePath: configDir,
+      },
+    });
+  });
+
+  test('Load config.cjs with defineConfig in cjs project', async () => {
+    const fixtureDir = join(__dirname, 'config/cjs');
+    const configDir = join(fixtureDir, 'rslib.config.cjs');
+    const config = await loadConfig(configDir);
+    expect(config).toEqual({
+      lib: [],
+      source: {
+        entry: {
+          main: './foo/index.js',
+        },
+      },
+      _privateMeta: {
+        configFilePath: configDir,
+      },
+    });
+  });
+
+  test('Load config.js in esm project', async () => {
+    const fixtureDir = join(__dirname, 'config/esm');
+    const configDir = join(fixtureDir, 'rslib.config.js');
+    const config = await loadConfig(configDir);
+    expect(config).toEqual({
+      lib: [],
+      source: {
+        entry: {
+          main: './foo/index.js',
+        },
+      },
+      _privateMeta: {
+        configFilePath: configDir,
+      },
+    });
+  });
+
+  test('Load config.cjs in esm project', async () => {
+    const fixtureDir = join(__dirname, 'config/esm');
+    const configDir = join(fixtureDir, 'rslib.config.cjs');
+    const config = await loadConfig(configDir);
+    expect(config).toEqual({
+      lib: [],
+      source: {
+        entry: {
+          main: './foo/index.js',
+        },
+      },
+      _privateMeta: {
+        configFilePath: configDir,
+      },
+    });
+  });
+
+  test('Load config.ts in esm project', async () => {
+    const fixtureDir = join(__dirname, 'config/esm');
+    const configDir = join(fixtureDir, 'rslib.config.ts');
+    const config = await loadConfig(configDir);
+    expect(config).toEqual({
+      lib: [],
+      source: {
+        entry: {
+          main: './foo/index.ts',
+        },
+      },
+      _privateMeta: {
+        configFilePath: configDir,
+      },
+    });
+  });
+
+  test('Load config.mjs with defineConfig in esm project', async () => {
+    const fixtureDir = join(__dirname, 'config/esm');
+    const configDir = join(fixtureDir, 'rslib.config.mjs');
+    const config = await loadConfig(configDir);
+    expect(config).toEqual({
+      lib: [],
+      source: {
+        entry: {
+          main: './foo/index.js',
+        },
+      },
+      _privateMeta: {
+        configFilePath: configDir,
+      },
+    });
+  });
+});
+
+describe('Should compose create Rsbuild config correctly', () => {
+  test('Merge Rsbuild config', async () => {
+    const rslibConfig: RslibConfig = {
+      lib: [
+        {
+          format: 'esm',
+          source: {
+            alias: {
+              foo: 'foo/esm',
+            },
+            preEntry: './b.js',
+          },
+        },
+        {
+          format: 'cjs',
+          source: {
+            alias: {
+              bar: 'bar/cjs',
+            },
+            preEntry: ['./c.js', './d.js'],
+          },
+        },
+        {
+          format: 'umd',
+        },
+      ],
+      source: {
+        alias: {
+          foo: 'foo',
+          bar: 'bar',
+        },
+        preEntry: './a.js',
+      },
+      output: {
+        filenameHash: false,
+        minify: true,
+      },
+    };
+    const composedRsbuildConfig = await composeCreateRsbuildConfig(rslibConfig);
+    expect(composedRsbuildConfig).toMatchSnapshot();
+  });
+});
diff --git a/packages/core/tests/config/cjs/package.json b/packages/core/tests/config/cjs/package.json
new file mode 100644
index 000000000..5bbefffba
--- /dev/null
+++ b/packages/core/tests/config/cjs/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}
diff --git a/packages/core/tests/config/cjs/rslib.config.cjs b/packages/core/tests/config/cjs/rslib.config.cjs
new file mode 100644
index 000000000..aa2b913a6
--- /dev/null
+++ b/packages/core/tests/config/cjs/rslib.config.cjs
@@ -0,0 +1,10 @@
+const { defineConfig } = require('../../../../core/src/config');
+
+module.exports = defineConfig((args) => ({
+  lib: [],
+  source: {
+    entry: {
+      main: './foo/index.js',
+    },
+  },
+}));
diff --git a/packages/core/tests/config/cjs/rslib.config.js b/packages/core/tests/config/cjs/rslib.config.js
new file mode 100644
index 000000000..2138d4cdd
--- /dev/null
+++ b/packages/core/tests/config/cjs/rslib.config.js
@@ -0,0 +1,8 @@
+module.exports = {
+  lib: [],
+  source: {
+    entry: {
+      main: './foo/index.js',
+    },
+  },
+};
diff --git a/packages/core/tests/config/cjs/rslib.config.mjs b/packages/core/tests/config/cjs/rslib.config.mjs
new file mode 100644
index 000000000..3d824b6e9
--- /dev/null
+++ b/packages/core/tests/config/cjs/rslib.config.mjs
@@ -0,0 +1,8 @@
+export default {
+  lib: [],
+  source: {
+    entry: {
+      main: './foo/index.js',
+    },
+  },
+};
diff --git a/packages/core/tests/config/cjs/rslib.config.ts b/packages/core/tests/config/cjs/rslib.config.ts
new file mode 100644
index 000000000..e23ab3976
--- /dev/null
+++ b/packages/core/tests/config/cjs/rslib.config.ts
@@ -0,0 +1,8 @@
+export default {
+  lib: [],
+  source: {
+    entry: {
+      main: './foo/index.ts',
+    },
+  },
+};
diff --git a/packages/core/tests/config/esm/package.json b/packages/core/tests/config/esm/package.json
new file mode 100644
index 000000000..3dbc1ca59
--- /dev/null
+++ b/packages/core/tests/config/esm/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
diff --git a/packages/core/tests/config/esm/rslib.config.cjs b/packages/core/tests/config/esm/rslib.config.cjs
new file mode 100644
index 000000000..2138d4cdd
--- /dev/null
+++ b/packages/core/tests/config/esm/rslib.config.cjs
@@ -0,0 +1,8 @@
+module.exports = {
+  lib: [],
+  source: {
+    entry: {
+      main: './foo/index.js',
+    },
+  },
+};
diff --git a/packages/core/tests/config/esm/rslib.config.js b/packages/core/tests/config/esm/rslib.config.js
new file mode 100644
index 000000000..3d824b6e9
--- /dev/null
+++ b/packages/core/tests/config/esm/rslib.config.js
@@ -0,0 +1,8 @@
+export default {
+  lib: [],
+  source: {
+    entry: {
+      main: './foo/index.js',
+    },
+  },
+};
diff --git a/packages/core/tests/config/esm/rslib.config.mjs b/packages/core/tests/config/esm/rslib.config.mjs
new file mode 100644
index 000000000..facaa7ee5
--- /dev/null
+++ b/packages/core/tests/config/esm/rslib.config.mjs
@@ -0,0 +1,10 @@
+import { defineConfig } from '../../../../core/src/config';
+
+export default defineConfig((args) => ({
+  lib: [],
+  source: {
+    entry: {
+      main: './foo/index.js',
+    },
+  },
+}));
diff --git a/packages/core/tests/config/esm/rslib.config.ts b/packages/core/tests/config/esm/rslib.config.ts
new file mode 100644
index 000000000..e23ab3976
--- /dev/null
+++ b/packages/core/tests/config/esm/rslib.config.ts
@@ -0,0 +1,8 @@
+export default {
+  lib: [],
+  source: {
+    entry: {
+      main: './foo/index.ts',
+    },
+  },
+};