[refactor] Extract some test helpers for certificate verification unittests.

net/cert/internal/test_helpers.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_CERT_INTERNAL_TEST_HELPERS_H_
+#define NET_CERT_INTERNAL_TEST_HELPERS_H_
+
+#include <string>
+#include <vector>
+
+#include "net/der/input.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace net {
+
+// Creates a der::Input from an std::string. The lifetimes are a bit subtle
+// when using this function:
+//
+// The returned der::Input() is only valid so long as the input string is alive
+// and is not mutated.
+//
+// Note that the input parameter has been made a pointer to prevent callers
+// from accidentally passing an r-value.
+der::Input InputFromString(const std::string* s);
+
+// Helper structure that maps a PEM block header (for instance "CERTIFICATE") to
+// the destination where the value for that block should be written.
+struct PemBlockMapping {
+  const char* block_name;
+  std::string* value;
+};
+
+// ReadTestDataFromPemFile() is a helper function that reads a PEM test file
+// rooted in the "src/" directory.
+//
+//   * file_path_ascii:
+//       The path to the PEM file, relative to src. For instance
+//       "net/data/verify_signed_data_unittest/foopy.pem"
+//
+//   * mappings:
+//       An array of length |mappings_length| which maps the expected PEM
+//       headers to the destination to write its data.
+//
+// The function ensures that each of the chosen mappings is satisfied exactly
+// once. In other words, the header must be present, have valid data, and
+// appear no more than once.
+::testing::AssertionResult ReadTestDataFromPemFile(
+    const std::string& file_path_ascii,
+    const PemBlockMapping* mappings,
+    size_t mappings_length);
+
+// This is the same as the variant above, however it uses template magic so an
+// mappings array can be passed in directly (and the correct length is
+// inferred).
+template <size_t N>
+::testing::AssertionResult ReadTestDataFromPemFile(
+    const std::string& file_path_ascii,
+    const PemBlockMapping(&mappings)[N]) {
+  return ReadTestDataFromPemFile(file_path_ascii, mappings, N);
+}
+
+}  // namespace net
+
+#endif  // NET_CERT_INTERNAL_TEST_HELPERS_H_