1 files changed, 41 insertions, 0 deletions
diff --git a/test/internal/group-by.spec.ts b/test/internal/group-by.spec.ts
new file mode 100644
index 00000000..4f186e3d
--- /dev/null
+++ b/test/internal/group-by.spec.ts
@@ -0,0 +1,41 @@
+import { describe, expect, it } from 'vitest';
+import { groupBy } from '../../src/internal/group-by';
+
+describe('groupBy()', () => {
+  it('should group values by key', () => {
+    const values = [
+      { id: 1, name: 'John' },
+      { id: 2, name: 'Jane' },
+      { id: 3, name: 'John' },
+    ];
+
+    const result = groupBy(values, ({ name }) => name);
+
+    expect(result).toEqual({
+      John: [
+        { id: 1, name: 'John' },
+        { id: 3, name: 'John' },
+      ],
+      Jane: [{ id: 2, name: 'Jane' }],
+    });
+  });
+
+  it('should group by key and map values', () => {
+    const values = [
+      { id: 1, name: 'John' },
+      { id: 2, name: 'Jane' },
+      { id: 3, name: 'John' },
+    ];
+
+    const result = groupBy(
+      values,
+      ({ name }) => name,
+      ({ id }) => id
+    );
+
+    expect(result).toEqual({
+      John: [1, 3],
+      Jane: [2],
+    });
+  });
+});