2 files changed, 70 insertions, 2 deletions

diff --git a/src/mongo/unittest/unittest.cpp b/src/mongo/unittest/unittest.cpp
index e728ced46b1..feb9a2aeb05 100644
--- a/src/mongo/unittest/unittest.cpp
+++ b/src/mongo/unittest/unittest.cpp
@@ -36,6 +36,7 @@
 #include "mongo/base/init.h"
 #include "mongo/logger/console_appender.h"
 #include "mongo/logger/log_manager.h"
+#include "mongo/logger/logger.h"
 #include "mongo/logger/message_event_utf8_encoder.h"
 #include "mongo/logger/message_log_domain.h"
 #include "mongo/util/assert_util.h"
@@ -111,8 +112,13 @@ namespace mongo {
 
         Result* Result::cur = 0;
 
-        Test::Test() {}
-        Test::~Test() {}
+        Test::Test() : _isCapturingLogMessages(false) {}
+
+        Test::~Test() {
+            if (_isCapturingLogMessages) {
+                stopCapturingLogMessages();
+            }
+        }
 
         void Test::run() {
             setUp();
@@ -139,6 +145,40 @@ namespace mongo {
         void Test::setUp() {}
         void Test::tearDown() {}
 
+namespace {
+    class StringVectorAppender : public logger::MessageLogDomain::EventAppender {
+    public:
+        explicit StringVectorAppender(std::vector<std::string>* lines) : _lines(lines) {}
+        virtual ~StringVectorAppender() {}
+        virtual Status append(const logger::MessageLogDomain::Event& event) {
+            std::ostringstream _os;
+            if (!_encoder.encode(event, _os)) {
+                return Status(ErrorCodes::LogWriteFailed, "Failed to append to LogTestAppender.");
+            }
+            _lines->push_back(_os.str());
+            return Status::OK();
+        }
+    private:
+        logger::MessageEventDetailsEncoder _encoder;
+        std::vector<std::string>* _lines;
+    };
+}  // namespace
+
+        void Test::startCapturingLogMessages() {
+            invariant(!_isCapturingLogMessages);
+            _capturedLogMessages.clear();
+            _captureAppenderHandle = logger::globalLogDomain()->attachAppender(
+                    logger::MessageLogDomain::AppenderAutoPtr(new StringVectorAppender(
+                                                                      &_capturedLogMessages)));
+            _isCapturingLogMessages = true;
+        }
+
+        void Test::stopCapturingLogMessages() {
+            invariant(_isCapturingLogMessages);
+            logger::globalLogDomain()->detachAppender(_captureAppenderHandle);
+            _isCapturingLogMessages = false;
+        }
+
         Suite::Suite( const std::string& name ) : _name( name ) {
             registerSuite( name , this );
         }
diff --git a/src/mongo/unittest/unittest.h b/src/mongo/unittest/unittest.h
index 8e27707b391..ccef6dc9925 100644
--- a/src/mongo/unittest/unittest.h
+++ b/src/mongo/unittest/unittest.h
@@ -45,6 +45,7 @@
 
 #include "mongo/base/status_with.h"
 #include "mongo/logger/logstream_builder.h"
+#include "mongo/logger/message_log_domain.h"
 #include "mongo/stdx/functional.h"
 #include "mongo/util/assert_util.h"
 #include "mongo/util/mongoutils/str.h"
@@ -263,6 +264,29 @@ namespace mongo {
             class FixtureExceptionForTesting : public std::exception {
             };
 
+            /**
+             * Starts capturing messages logged by code under test.
+             *
+             * Log messages will still also go to their default destination; this
+             * code simply adds an additional sink for log messages.
+             *
+             * Clears any previously captured log lines.
+             */
+            void startCapturingLogMessages();
+
+            /**
+             * Stops capturing log messages logged by code under test.
+             */
+            void stopCapturingLogMessages();
+
+            /**
+             * Gets a vector of strings, one log line per string, captured since
+             * the last call to startCapturingLogMessages() in this test.
+             */
+            const std::vector<std::string>& getCapturedLogMessages() const {
+                return _capturedLogMessages;
+            }
+
         private:
             /**
              * Called on the test object before running the test.
@@ -278,6 +302,10 @@ namespace mongo {
              * The test itself.
              */
             virtual void _doTest() = 0;
+
+            bool _isCapturingLogMessages;
+            std::vector<std::string> _capturedLogMessages;
+            logger::MessageLogDomain::AppenderHandle _captureAppenderHandle;
         };
 
         /**