Page.WaitForFunctionAsync should work with multiline strings (#914)

* Page.WaitForFunctionAsync should work with multiline strings

* Add tests

Author: kblok

lib/PuppeteerSharp.Tests/PageTests/WaitForTests.cs

@@ -56,6 +56,15 @@ public async Task ShouldTimeout()
             Assert.True((DateTime.Now - startTime).TotalMilliseconds > timeout / 2);
         }
 
+        [Fact]
+        public async Task ShouldWorkWithMultilineBody()
+        {
+            var result = await Page.WaitForExpressionAsync(@"
+                (() => true)()
+            ");
+            Assert.True(await result.JsonValueAsync<bool>());
+        }
+
         [Fact]
         public async Task ShouldWaitForPredicate()
         {
@@ -66,8 +75,6 @@ public async Task ShouldWaitForPredicate()
 
         [Fact]
         public async Task ShouldWaitForPredicateWithArguments()
-        {
-            await Page.WaitForFunctionAsync("(arg1, arg2) => arg1 !== arg2", new WaitForFunctionOptions(), 1, 2);
-        }
+            => await Page.WaitForFunctionAsync("(arg1, arg2) => arg1 !== arg2", new WaitForFunctionOptions(), 1, 2);
     }
 }

lib/PuppeteerSharp/WaitTask.cs

@@ -130,7 +130,7 @@ internal WaitTask(
             }
 
             _frame = frame;
-            _predicateBody = isExpression ? $"return {predicateBody}" : $"return ( {predicateBody} )(...args)";
+            _predicateBody = isExpression ? $"return ({predicateBody})" : $"return ({predicateBody})(...args)";
             _polling = polling;
             _pollingInterval = pollingInterval;
             _timeout = timeout;