Eliminate the dependency on kernel pseudo-files when running unit tests

log_unit_tests.cc

Index: log_unit_tests.cc
diff --git a/log_unit_tests.cc b/log_unit_tests.cc
index 2d279eef679bd45cde569aea19b20bd30aa6dc7b..b12718a20fad934aa44b3e99f67d9aad510bf8da 100644
--- a/log_unit_tests.cc
+++ b/log_unit_tests.cc
@@ -3,8 +3,13 @@
 // found in the LICENSE file.
 
 #include "bootstat.h"
+#include "bootstat_test.h"
 
 #include <errno.h>
+#include <stdlib.h>
+#include <sys/fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 #include <unistd.h>
 
 #include <string>
@@ -16,40 +21,245 @@ namespace {
 
 using std::string;
 
-static const char kMostVoluminousEventName[] =
-  //             16              32              48              64
-  "event-6789abcdef_123456789ABCDEF.123456789abcdef0123456789abcdef" //  64
-  "event-6789abcdef_123456789ABCDEF.123456789abcdef0123456789abcdef" // 128
-  "event-6789abcdef_123456789ABCDEF.123456789abcdef0123456789abcdef" // 191
-  "event-6789abcdef_123456789ABCDEF.123456789abcdef0123456789abcdef" // 256
-  ;
+static void RemoveFile(const string& file_path) {
+  EXPECT_EQ(0, unlink(file_path.c_str()))
+      << "can't unlink file " << file_path << ": "
+      << strerror(errno);
+}
+
+
+// Class to track and test the data associated with a single event.
+// The primary function is TestLogEvent():  This method wraps calls
+// to bootstat_log() with code to track the expected contents of the
+// event files.  After logging, the expected content is tested
+// against the actual content.
+class EventTracker {
+  public:
+    EventTracker(const string& name, const string& uptime_prefix,
+               const string& disk_prefix);
+    void TestLogEvent(const string& uptime, const string& diskstats);
+    void Reset();
+
+  private:
+    string event_name_;
+    string uptime_file_name_;
+    string uptime_content_;
+    string diskstats_file_name_;
+    string diskstats_content_;
+};
+
+
+EventTracker::EventTracker(const string& name,
+                           const string& uptime_prefix,
+                           const string& diskstats_prefix)
+    : event_name_(name),
+      uptime_content_(""),
+      diskstats_content_("") {
+  string truncated_name =
+      event_name_.substr(0, BOOTSTAT_MAX_EVENT_LEN - 1);
+  uptime_file_name_ = uptime_prefix + truncated_name;
+  diskstats_file_name_ = diskstats_prefix + truncated_name;
+}
+
+
+// Basic helper function to test whether the contents of the
+// specified file exactly match the given contents string.
+static void ValidateEventFileContents(const string& file_name,
+                                      const string& file_contents) {
+  int rv = access(file_name.c_str(), W_OK);
+  EXPECT_EQ(0, rv) << file_name << " is not writable: "
+                   << strerror(errno);
+  rv = access(file_name.c_str(), R_OK);
+  ASSERT_EQ(0, rv) << file_name << " is not readable: "
+                   << strerror(errno);
+  char *buffer = new char[file_contents.length() + 1];
+  int fd = open(file_name.c_str(), O_RDONLY);
+  rv = read(fd, buffer, file_contents.length());
+  EXPECT_EQ(file_contents.length(), rv);
+  buffer[file_contents.length()] = '\0';
+  string actual_contents(buffer);
+  EXPECT_EQ(file_contents, actual_contents);
+  rv = read(fd, buffer, 1);
+  EXPECT_EQ(0, rv) << "found data in event file past expected EOF";
+  (void)close(fd);
+  delete buffer;
+}
 
-static const string kUptimeFileNamePrefix("/tmp/uptime-");
-static const string kDiskStatFileNamePrefix("/tmp/disk-");
 
-static void TestEventFileAccess(const string& file_name) {
-  int rv = access(file_name.c_str(), R_OK | W_OK);
-  EXPECT_EQ(rv, 0) << "access to " << file_name
-                   << " failed: " << strerror(errno);
-  (void) unlink(file_name.c_str());
+// Call bootstat_log() once, and update the expected content for
+// this event.  Test that the new content of the event's files
+// matches the updated expected content.
+void EventTracker::TestLogEvent(const string& uptime,
+                                const string& diskstats) {
+  bootstat_log(event_name_.c_str());
+  uptime_content_ += uptime;
+  diskstats_content_ += diskstats;
+  ValidateEventFileContents(uptime_file_name_, uptime_content_);
+  ValidateEventFileContents(diskstats_file_name_, diskstats_content_);
 }
 
-static void TestEventByName(const string& event_name) {
-  bootstat_log(event_name.c_str());
-  string truncated_event(event_name.substr(0, BOOTSTAT_MAX_EVENT_LEN - 1));
-  TestEventFileAccess(kUptimeFileNamePrefix + truncated_event);
-  TestEventFileAccess(kDiskStatFileNamePrefix + truncated_event);
+
+// Reset event state back to initial conditions, by deleting the
+// associated event files, and clearing the expected contents.
+void EventTracker::Reset() {
+  uptime_content_.clear();
+  diskstats_content_.clear();
+  RemoveFile(diskstats_file_name_);
+  RemoveFile(uptime_file_name_);
+}
+
+
+// Bootstat test class.  We use this class to override the
+// dependencies in bootstat_log() on the file paths for /proc/uptime
+// and /sys/block/<device>/stat.
+//
+// The class uses test-specific interfaces that change the default
+// paths from the kernel statistics psuedo-files to temporary paths
+// selected by this test.  This class also redirects the location for
+// the event files created by bootstat_log() to a temporary directory.
+class BootstatTest : public ::testing::Test {
+  protected:
+    virtual void SetUp();
+    virtual void TearDown();
+
+    EventTracker MakeEvent(const string& event_name) {
+      return EventTracker(event_name, uptime_event_prefix_,
+                          disk_event_prefix_);
+    }
+
+    void SetStatsContent(const char* uptime_content,
+                         const char* disk_content);
+    void TestLogEvent(EventTracker& event);
+
+  private:
+    string stats_output_dir_;
+    string uptime_event_prefix_;
+    string disk_event_prefix_;
+
+    string uptime_stats_file_name_;
+    string uptime_stats_content_;
+    string disk_stats_file_name_;
+    string disk_stats_content_;
+};
+
+
+void BootstatTest::SetUp() {
+  char dir_template[] = "bootstat_test_XXXXXX";
+  stats_output_dir_ = string(mkdtemp(dir_template));
+  uptime_event_prefix_ = stats_output_dir_ + "/uptime-";
+  disk_event_prefix_ = stats_output_dir_ + "/disk-";
+  uptime_stats_file_name_ = stats_output_dir_ + "/proc_uptime";
+  disk_stats_file_name_ = stats_output_dir_ + "/block_stats";
+  bootstat_set_output_directory(stats_output_dir_.c_str());
+  bootstat_set_uptime_file_name(uptime_stats_file_name_.c_str());
+  bootstat_set_disk_file_name(disk_stats_file_name_.c_str());
 }
 
-// Tests that name truncation of logged events works as advertised
-TEST(BoostatTest, EventNameTruncation) {
+
+void BootstatTest::TearDown() {
+  bootstat_set_uptime_file_name(NULL);
+  bootstat_set_disk_file_name(NULL);
+  bootstat_set_output_directory(NULL);
+  RemoveFile(uptime_stats_file_name_);
+  RemoveFile(disk_stats_file_name_);
+  EXPECT_EQ(0, rmdir(stats_output_dir_.c_str()))
+      << "Can't remove directory " << stats_output_dir_
+      << ": " << strerror(errno) << ".";
+}
+
+
+static void WriteStatsContent(const string& content, const string& file_path) {
+  const int kFileOpenFlags = O_WRONLY | O_TRUNC | O_CREAT;
+  const mode_t kFileCreationMode =
+      S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
+  int fd = open(file_path.c_str(), kFileOpenFlags, kFileCreationMode);
+  int nwrite = write(fd, content.c_str(), content.length());
+  EXPECT_EQ(content.length(), nwrite)
+      << "write to stats file " << file_path
+      << " failed: " << strerror(errno);
+  (void)close(fd);
+}
+
+
+// Set the content of the files mocking the contents of the kernel's
+// statistics pseudo-files.  The strings provided here will be the
+// ones recorded for subsequent calls to bootstat_log() for all
+// events.
+void BootstatTest::SetStatsContent(const char* uptime_stats,
+                                   const char* disk_stats) {
+  uptime_stats_content_ = string(uptime_stats);
+  WriteStatsContent(uptime_stats_content_, uptime_stats_file_name_);
+  disk_stats_content_ = string(disk_stats);
+  WriteStatsContent(disk_stats_content_, disk_stats_file_name_);
+}
+
+
+void BootstatTest::TestLogEvent(EventTracker& event) {
+  event.TestLogEvent(uptime_stats_content_, disk_stats_content_);
+}
+
+
+// Test data to be used as input to SetStatsContent().
+//
+// The structure of this array is pairs of strings, terminated by a
+// single NULL.  The first string in the pair is content for
+// /proc/uptime, the second for /sys/block/<device>/stat.
+//
+// This data is taken directly from a development system, and is
+// representative of valid stats content, though not typical of what
+// would be seen immediately after boot.
+static const char* bootstat_data[] = {
+/*  0  */
+/* uptime */  "691448.42 11020440.26\n",
+/*  disk  */  " 1417116    14896 55561564 10935990  4267850 78379879"
+                  " 661568738 1635920520      158 17856450 1649520570\n",
+/*  1  */
+/* uptime */  "691623.71 11021372.99\n",
+/*  disk  */  " 1420714    14918 55689988 11006390  4287385 78594261"
+                  " 663441564 1651579200      152 17974280 1665255160\n",
+/* EOT */     NULL
+};
+
+
+// Tests that event file content matches expectations when an
+// event is logged multiple times.
+TEST_F(BootstatTest, ContentGeneration) {
+  EventTracker ev = MakeEvent(string("test_event"));
+  int i = 0;
+  while (bootstat_data[i] != NULL) {
+    SetStatsContent(bootstat_data[i], bootstat_data[i+1]);
+    TestLogEvent(ev);
+    i += 2;
+  }
+  ev.Reset();
+}
+
+
+// Tests that name truncation of logged events works as advertised.
+TEST_F(BootstatTest, EventNameTruncation) {
+  static const char kMostVoluminousEventName[] =
+    //             16              32              48              64
+    "event-6789abcdef_123456789ABCDEF.123456789abcdef0123456789abcdef" //  64
+    "=064+56789abcdef_123456789ABCDEF.123456789abcdef0123456789abcdef" // 128
+    "=128+56789abcdef_123456789ABCDEF.123456789abcdef0123456789abcdef" // 191
+    "=191+56789abcdef_123456789ABCDEF.123456789abcdef0123456789abcdef" // 256
+    ;
+
   string very_long(kMostVoluminousEventName);
+  SetStatsContent(bootstat_data[0], bootstat_data[1]);
 
-  TestEventByName(very_long);
-  TestEventByName(very_long.substr(0, 1));
-  TestEventByName(very_long.substr(0, 16));
-  TestEventByName(very_long.substr(0, BOOTSTAT_MAX_EVENT_LEN - 1));
-  TestEventByName(very_long.substr(0, BOOTSTAT_MAX_EVENT_LEN));
+  EventTracker ev = MakeEvent(very_long);
+  TestLogEvent(ev);
+  ev.Reset();
+  ev = MakeEvent(very_long.substr(0, 1));
+  TestLogEvent(ev);
+  ev.Reset();
+  ev = MakeEvent(very_long.substr(0, BOOTSTAT_MAX_EVENT_LEN - 1));
+  TestLogEvent(ev);
+  ev.Reset();
+  ev = MakeEvent(very_long.substr(0, BOOTSTAT_MAX_EVENT_LEN));
+  TestLogEvent(ev);
+  ev.Reset();
 }
 
 }  // namespace