diff --git a/README.md b/README.md
index db2a4433..b82e4233 100644
--- a/README.md
+++ b/README.md
@@ -89,6 +89,19 @@ This is the Stackdriver metadata agent.
        $ cd src
        $ make -j10
 
+# Testing
+
+1. Run all tests:
+
+       $ cd src
+       $ make test
+
+2. Run individual tests:
+
+       $ cd test
+       $ make <test_name>
+       $ ./<test_name>
+
 # Packaging
 
 1. Build the DEB package:
diff --git a/src/.gitignore b/src/.gitignore
index 7ab262d8..4dee5759 100644
--- a/src/.gitignore
+++ b/src/.gitignore
@@ -1,4 +1,4 @@
-metadatad
 init-submodules
 build-cpp-netlib
 build-yaml-cpp
+metadatad
diff --git a/src/Makefile b/src/Makefile
index da123cd7..afc41b43 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -60,6 +60,9 @@ INSTALL_DATA=$(INSTALL) -m 644
 metadatad: $(LIBS) $(OBJS)
 	$(CXX) -o $@ $(LDFLAGS) $^ $(LDLIBS)
 
+test:
+	cd ../test && $(MAKE) test
+
 $(OBJS): init-submodules
 
 install: metadatad
diff --git a/src/time.cc b/src/time.cc
index 9f60454c..687fad8c 100644
--- a/src/time.cc
+++ b/src/time.cc
@@ -16,6 +16,8 @@
 
 #include "time.h"
 
+#include <cctype>
+#include <cmath>
 #include <cstdlib>
 #include <iomanip>
 #include <mutex>
@@ -31,8 +33,11 @@ namespace {
 // See http://stackoverflow.com/questions/4137748.
 int UTCOffset() {
   const std::time_t local = std::time(nullptr);
-  const std::time_t utc = std::mktime(std::gmtime(&local));
-  return utc - local;
+  std::tm utc_time = safe_gmtime(&local);
+  // Since we're only using this for conversion to UTC, always turn off DST.
+  utc_time.tm_isdst = 0;
+  const std::time_t utc = std::mktime(&utc_time);
+  return local - utc;
 }
 
 const int kUtcOffset = UTCOffset();
@@ -57,17 +62,36 @@ std::string ToString(const std::chrono::system_clock::time_point& t) {
 
 std::chrono::system_clock::time_point FromString(const std::string& s) {
   std::tm tm;
-  const char* end = strptime(s.c_str(), "%Y-%m-%dT%H:%M:%S", &tm);
-  if (end == nullptr || end - s.c_str() != s.find('.')) {
-    // TODO
+  char* const end = strptime(s.c_str(), "%Y-%m-%dT%H:%M:%S", &tm);
+  if (end == nullptr || !std::isdigit(*(end - 2))) {
+    // TODO: Invalid time format.
     return std::chrono::system_clock::time_point();
   }
   char* zone;
-  long ns = std::strtol(end + 1, &zone, 10);
-  if (zone <= end + 1 || *zone != 'Z' || *(zone+1) != '\0') {
-    // TODO
+  if (*end == '.') {
+    (void)std::strtol(end + 1, &zone, 10);
+    if (zone <= end + 1) {
+      // TODO: Missing nanoseconds.
+      return std::chrono::system_clock::time_point();
+    }
+  } else {
+    zone = end;
+  }
+  if (*zone != 'Z' || *(zone+1) != '\0') {
+    // TODO: Invalid timezone.
+    return std::chrono::system_clock::time_point();
+  }
+  char* d_end;
+  double seconds = std::strtod(end - 2, &d_end);
+  if (d_end != zone) {
+    // TODO: Internal error.
     return std::chrono::system_clock::time_point();
   }
+  static_assert(sizeof(long) == 8, "long is too small");
+  // Truncate to 9 digits by rounding to 10 and discarding the last one.
+  long ns = std::lround((seconds - tm.tm_sec) * 10000000000) / 10;
+  // Our UTC offset constant assumes no DST.
+  tm.tm_isdst = 0;
   const std::time_t local_time = std::mktime(&tm);
   const std::time_t utc_time = local_time + kUtcOffset;
   std::chrono::system_clock::time_point sec =
diff --git a/test/.gitignore b/test/.gitignore
new file mode 100644
index 00000000..d16f2f56
--- /dev/null
+++ b/test/.gitignore
@@ -0,0 +1,2 @@
+init-submodules
+*_unittest
diff --git a/test/Makefile b/test/Makefile
index 5b33fc2a..efea1665 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -21,8 +21,9 @@ TEST_DIR=.
 TEST_SOURCES=$(wildcard $(TEST_DIR)/*_unittest.cc)
 TEST_OBJS=$(TEST_SOURCES:$(TEST_DIR)/%.cc=%.o)
 TESTS=\
+      base64_unittest \
       format_unittest \
-      base64_unittest
+      time_unittest
 
 GTEST_LIB=gtest_lib.a
 
@@ -47,7 +48,6 @@ init-submodules:
 	git submodule update --init $(GTEST_MODULE)
 	touch init-submodules
 
-
 $(SRC_DIR)/%.o: $(SRC_DIR)/%.cc
 	cd $(SRC_DIR) && $(MAKE) $(@:$(SRC_DIR)/%=%)
 
@@ -67,4 +67,7 @@ format_unittest: $(GTEST_LIB) format_unittest.o $(SRC_DIR)/format.o
 base64_unittest: $(GTEST_LIB) base64_unittest.o $(SRC_DIR)/base64.o
 	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
 
+time_unittest: $(GTEST_LIB) time_unittest.o $(SRC_DIR)/time.o
+	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
+
 .PHONY: all test clean purge
diff --git a/test/time_unittest.cc b/test/time_unittest.cc
new file mode 100644
index 00000000..cc478b1a
--- /dev/null
+++ b/test/time_unittest.cc
@@ -0,0 +1,160 @@
+#include "../src/time.h"
+#include "gtest/gtest.h"
+
+using namespace google;
+
+namespace {
+
+TEST(TimeTest, EpochToString) {
+  const std::chrono::system_clock::time_point epoch;
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(epoch)
+  );
+}
+
+TEST(TimeTest, RoundtripViaTimePoint) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:45.678901234Z");
+  EXPECT_EQ(
+      "2018-03-03T01:23:45.678901234Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, RoundtripViaString) {
+  const std::chrono::system_clock::time_point t =
+      std::chrono::system_clock::now();
+  EXPECT_EQ(
+      t,
+      rfc3339::FromString(rfc3339::ToString(t))
+  );
+}
+
+TEST(TimeTest, FromStringNoNanos) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:45Z");
+  EXPECT_EQ(
+      "2018-03-03T01:23:45.000000000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringFewerDigits) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:45.6789Z");
+  EXPECT_EQ(
+      "2018-03-03T01:23:45.678900000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringMoreDigits) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:45.67890123456789Z");
+  EXPECT_EQ(
+      "2018-03-03T01:23:45.678901234Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringLargeNanos) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:45.9876543210987Z");
+  EXPECT_EQ(
+      "2018-03-03T01:23:45.987654321Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringPositiveNanos) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:45.+678901234Z");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringNegativeNanos) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:45.-678901234Z");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringPositiveSeconds) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:+4.567890123Z");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringNegativeSeconds) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:-4.567890123Z");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringHexSeconds) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:0x45.678901234Z");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringInfSeconds) {
+  const std::chrono::system_clock::time_point t1 =
+      rfc3339::FromString("2018-03-03T01:23:+infZ");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t1)
+  );
+  const std::chrono::system_clock::time_point t2 =
+      rfc3339::FromString("2018-03-03T01:23:-infZ");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t2)
+  );
+  const std::chrono::system_clock::time_point t3 =
+      rfc3339::FromString("2018-03-03T01:23:+nanZ");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t3)
+  );
+  const std::chrono::system_clock::time_point t4 =
+      rfc3339::FromString("2018-03-03T01:23:-nanZ");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t4)
+  );
+}
+
+TEST(TimeTest, FromStringTooManySeconds) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:1045.678901234Z");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+TEST(TimeTest, FromStringScientificSeconds) {
+  const std::chrono::system_clock::time_point t =
+      rfc3339::FromString("2018-03-03T01:23:45e+0Z");
+  EXPECT_EQ(
+      "1970-01-01T00:00:00.000000000Z",
+      rfc3339::ToString(t)
+  );
+}
+
+}