Improve the style of tests.

test/very_long_input.dart

Index: test/very_long_input.dart
diff --git a/test/very_long_input.dart b/test/very_long_input.dart
deleted file mode 100644
index b3e72b3e00f1761b2ce686bfde60f466bcb47c4d..0000000000000000000000000000000000000000
--- a/test/very_long_input.dart
+++ /dev/null
@@ -1,14 +0,0 @@
-library very_long_input_test;
-
-import 'package:crypto/crypto.dart';
-import 'package:test/test.dart';
-
-veryLongInput(digester, int byteLength, String verify) {
-  var nullCharacter = '\u0000'.codeUnitAt(0);
-  var input = [nullCharacter];
-  for (var i = 0; i < byteLength; i++) {
-    digester.add(input);
-  }
-  var d = digester.close();
-  expect(CryptoUtils.bytesToHex(d), verify);
-}