Initial commit after splitting from main project

tests/ComposeTest.php

@@ -0,0 +1,89 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tez\Utils\Tests\Fn;
+
+use PHPUnit\Framework\TestCase;
+use Tez\Utils\Fn\Compose;
+
+final class ComposeTest extends TestCase
+{
+    // -------------------------------------------------------------------------
+    // apply()
+    // -------------------------------------------------------------------------
+
+    public function testApplyExecutesRightToLeft(): void
+    {
+        $result = Compose::apply(
+            -3,
+            fn(int $n) => $n * 2,   // applied third: 4 * 2 = 8
+            fn(int $n) => $n + 1,   // applied second: 3 + 1 = 4
+            fn(int $n) => abs($n),  // applied first:  abs(-3) = 3
+        );
+
+        self::assertSame(8, $result);
+    }
+
+    public function testApplyWithNoFnsReturnsValueUnchanged(): void
+    {
+        self::assertSame(42, Compose::apply(42));
+    }
+
+    public function testApplyWithSingleFn(): void
+    {
+        self::assertSame('HELLO', Compose::apply('hello', 'strtoupper'));
+    }
+
+    public function testApplyRightToLeftOrderWithStrings(): void
+    {
+        // trim first, then strtolower, then replace spaces
+        $result = Compose::apply(
+            '  Hello World  ',
+            fn(string $s) => str_replace(' ', '-', $s),
+            'strtolower',
+            'trim',
+        );
+
+        self::assertSame('hello-world', $result);
+    }
+
+    // -------------------------------------------------------------------------
+    // build()
+    // -------------------------------------------------------------------------
+
+    public function testBuildReturnsReusableClosure(): void
+    {
+        $process = Compose::build(
+            fn(string $s) => str_replace(' ', '-', $s),
+            'strtolower',
+            'trim',
+        );
+
+        self::assertSame('hello-world', $process('  Hello World  '));
+        self::assertSame('foo-bar', $process('  FOO BAR  '));
+    }
+
+    public function testBuildWithNoFnsReturnsValueUnchanged(): void
+    {
+        $fn = Compose::build();
+
+        self::assertSame('hello', $fn('hello'));
+    }
+
+    public function testBuildReturnsClosure(): void
+    {
+        self::assertInstanceOf(\Closure::class, Compose::build('trim'));
+    }
+
+    public function testBuildIsEquivalentToPipelineWithReversedStages(): void
+    {
+        $double    = fn(int $n) => $n * 2;
+        $increment = fn(int $n) => $n + 1;
+        $absolute  = fn(int $n) => abs($n);
+
+        $composed = Compose::build($double, $increment, $absolute);
+
+        self::assertSame(8, $composed(-3));
+    }
+}