Use helper methods for running pub.

sdk/lib/_internal/pub/test/install/path/path_is_file_test.dart

Index: sdk/lib/_internal/pub/test/install/path/path_is_file_test.dart
diff --git a/sdk/lib/_internal/pub/test/install/path/path_is_file_test.dart b/sdk/lib/_internal/pub/test/install/path/path_is_file_test.dart
index 7779467b5c3a9fea6aa4409f816a11779db78827..dbbc0df245956b7d6be30738a4c316296928a034 100644
--- a/sdk/lib/_internal/pub/test/install/path/path_is_file_test.dart
+++ b/sdk/lib/_internal/pub/test/install/path/path_is_file_test.dart
@@ -10,7 +10,7 @@ import '../../test_pub.dart';
 
 main() {
   initConfig();
-  integration('path dependency when path is a d.file', () {
+  integration('path dependency when path is a file', () {
     d.dir('foo', [
       d.libDir('foo'),
       d.libPubspec('foo', '0.0.1')
@@ -28,15 +28,7 @@ main() {
       })
     ]).create();
 
-    // TODO(rnystrom): The "\" in a Windows path gets treated like a regex
-    // character, so hack escape. A better fix is to use a literal string
-    // instead of a RegExp to validate, but that requires us to move the
-    // stack traces out of the stderr when we invoke pub. See also: #4706.
-    var escapePath = dummyPath.replaceAll(r"\", r"\\");
-
-    schedulePub(args: ['install'],
-        error: new RegExp("Path dependency for package 'foo' must refer to a "
-                          "directory, not a file. Was '$escapePath'."),
-        exitCode: 1);
+    pubInstall(error: "Path dependency for package 'foo' must refer to a "
+                      "directory, not a file. Was '$dummyPath'.");
   });
 }