Validate number of required promises

lib/functions.php

@@ -445,12 +445,20 @@ namespace Amp\Promise {
      * @throws \Error If a non-Promise is in the array.
      */
     function some(array $promises, int $required = 1): Promise {
-        if (empty($promises)) {
-            return new Success([[], []]);
+        if ($required < 0) {
+            throw new \Error("Number of promises required must be non-negative");
         }
 
         $pending = \count($promises);
 
+        if ($required > $pending) {
+            throw new \Error("Too few promises provided");
+        }
+
+        if (empty($promises)) {
+            return new Success([[], []]);
+        }
+
         $deferred = new Deferred;
         $values = [];
         $exceptions = [];

test/SomeTest.php

@@ -11,7 +11,23 @@ use Amp\Loop;
 
 class SomeTest extends \PHPUnit\Framework\TestCase {
     public function testEmptyArray() {
-        $this->assertSame([[], []], Promise\wait(Promise\some([])));
+        $this->assertSame([[], []], Promise\wait(Promise\some([], 0)));
+    }
+
+    /**
+     * @expectedException \Error
+     * @expectedExceptionMessage Too few promises provided
+     */
+    public function testEmptyArrayWithNonZeroRequired() {
+        Promise\some([], 1);
+    }
+
+    /**
+     * @expectedException \Error
+     * @expectedExceptionMessage non-negative
+     */
+    public function testInvalidRequiredNumberOfPromises() {
+        Promise\some([], -1);
     }
 
     public function testSuccessfulPromisesArray() {