add js-fp3.tests

js-fp3.tests/patterns.test.js

@@ -0,0 +1,82 @@
+import { describe, it, expect, vi } from 'vitest';
+import { match, when, any } from '../js-fp3/library/patterns.js';
+
+describe('when', () => {
+  it('returns a two-element tuple of [predicate, handler]', () => {
+    const predicate = () => true;
+    const handler = () => 'result';
+
+    const branch = when(predicate, handler);
+
+    expect(branch).toEqual([predicate, handler]);
+  });
+});
+
+describe('any', () => {
+  it('returns true for any value', () => {
+    expect(any(0)).toBe(true);
+    expect(any(null)).toBe(true);
+    expect(any('string')).toBe(true);
+    expect(any({ x: 1 })).toBe(true);
+  });
+});
+
+describe('match', () => {
+  it('executes the handler of the first matching branch', () => {
+    const result = match(
+      when((v) => v === 1, () => 'one'),
+      when((v) => v === 2, () => 'two'),
+      when(any, () => 'other')
+    )(1);
+
+    expect(result).toBe('one');
+  });
+
+  it('falls through to the next branch when the first does not match', () => {
+    const result = match(
+      when((v) => v === 1, () => 'one'),
+      when((v) => v === 2, () => 'two'),
+      when(any, () => 'other')
+    )(2);
+
+    expect(result).toBe('two');
+  });
+
+  it('uses the any catch-all when no earlier branch matches', () => {
+    const result = match(
+      when((v) => v === 1, () => 'one'),
+      when(any, () => 'catch-all')
+    )(99);
+
+    expect(result).toBe('catch-all');
+  });
+
+  it('passes the value to the handler', () => {
+    const result = match(
+      when(any, (v) => v * 2)
+    )(7);
+
+    expect(result).toBe(14);
+  });
+
+  it('throws when no branch matches', () => {
+    expect(() =>
+      match(
+        when((v) => v === 1, () => 'one')
+      )(99)
+    ).toThrow('No matching pattern');
+  });
+
+  it('does not call handlers for branches that were not selected', () => {
+    const skipped = vi.fn(() => 'skipped');
+    const selected = vi.fn(() => 'selected');
+
+    match(
+      when((v) => v === 1, selected),
+      when(any, skipped)
+    )(1);
+
+    expect(selected).toHaveBeenCalledOnce();
+    expect(skipped).not.toHaveBeenCalled();
+  });
+});