Check in codegen test expectations.

test/codegen/expect/corelib/string_substring_test.js

+dart_library.library('corelib/string_substring_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__string_substring_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const string_substring_test = Object.create(null);
+  let VoidToString = () => (VoidToString = dart.constFn(dart.definiteFunctionType(core.String, [])))();
+  let dynamicTobool = () => (dynamicTobool = dart.constFn(dart.definiteFunctionType(core.bool, [dart.dynamic])))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  string_substring_test.main = function() {
+    expect$.Expect.equals(""[dartx.substring](0), "");
+    expect$.Expect.throws(dart.fn(() => ""[dartx.substring](1), VoidToString()), dart.fn(e => core.RangeError.is(e), dynamicTobool()));
+    expect$.Expect.throws(dart.fn(() => ""[dartx.substring](-1), VoidToString()), dart.fn(e => core.RangeError.is(e), dynamicTobool()));
+    expect$.Expect.equals("abc"[dartx.substring](0), "abc");
+    expect$.Expect.equals("abc"[dartx.substring](1), "bc");
+    expect$.Expect.equals("abc"[dartx.substring](2), "c");
+    expect$.Expect.equals("abc"[dartx.substring](3), "");
+    expect$.Expect.throws(dart.fn(() => "abc"[dartx.substring](4), VoidToString()), dart.fn(e => core.RangeError.is(e), dynamicTobool()));
+    expect$.Expect.throws(dart.fn(() => "abc"[dartx.substring](-1), VoidToString()), dart.fn(e => core.RangeError.is(e), dynamicTobool()));
+    expect$.Expect.equals(""[dartx.substring](0, null), "");
+    expect$.Expect.throws(dart.fn(() => ""[dartx.substring](1, null), VoidToString()), dart.fn(e => core.RangeError.is(e), dynamicTobool()));
+    expect$.Expect.throws(dart.fn(() => ""[dartx.substring](-1, null), VoidToString()), dart.fn(e => core.RangeError.is(e), dynamicTobool()));
+    expect$.Expect.equals("abc"[dartx.substring](0, null), "abc");
+    expect$.Expect.equals("abc"[dartx.substring](1, null), "bc");
+    expect$.Expect.equals("abc"[dartx.substring](2, null), "c");
+    expect$.Expect.equals("abc"[dartx.substring](3, null), "");
+    expect$.Expect.throws(dart.fn(() => "abc"[dartx.substring](4, null), VoidToString()), dart.fn(e => core.RangeError.is(e), dynamicTobool()));
+    expect$.Expect.throws(dart.fn(() => "abc"[dartx.substring](-1, null), VoidToString()), dart.fn(e => core.RangeError.is(e), dynamicTobool()));
+  };
+  dart.fn(string_substring_test.main, VoidTodynamic());
+  // Exports:
+  exports.string_substring_test = string_substring_test;
+});