PHPLIB-951: Assert operation before argument validation (#999)

This prevents a potential PHP warning for accessing a nonexistent array key if the operation doesn't exist, which was responsible for some Astrolabe test failures.

Since assertArgumentsBySchema() is called before the switch statement in Operation execute methods, we don't yet know that the operation exists. With this change, we should never hit default cases in those switch statements; however, they can remain in place for now.

tests/UnifiedSpecTests/Util.php

@@ -20,6 +20,7 @@
 use function array_key_exists;
 use function array_keys;
 use function implode;
+use function PHPUnit\Framework\assertArrayHasKey;
 use function PHPUnit\Framework\assertContains;
 use function PHPUnit\Framework\assertEmpty;
 use function PHPUnit\Framework\assertIsArray;
@@ -141,6 +142,8 @@ public static function assertHasOnlyKeys($arrayOrObject, array $keys): void
 
     public static function assertArgumentsBySchema(string $executingObjectName, string $operation, array $args): void
     {
+        assertArrayHasKey($executingObjectName, self::$args);
+        assertArrayHasKey($operation, self::$args[$executingObjectName]);
         self::assertHasOnlyKeys($args, self::$args[$executingObjectName][$operation]);
     }