Remove usage of CHECK_NOTNULL

We want to switch to absl logging instead of glog.  gtest and ceres are
going there, and we already have absl as a dependency.  ABSL doesn't
have CHECK_NOTNULL, and we can move things over in an easier to review
fashion.

Change-Id: Ifd9a11ec34a2357cec43f88dba015db9c28ed2cf
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/aos/events/logging/lzma_encoder_test.cc b/aos/events/logging/lzma_encoder_test.cc
index 60444d3..92b4f54 100644
--- a/aos/events/logging/lzma_encoder_test.cc
+++ b/aos/events/logging/lzma_encoder_test.cc
@@ -4,6 +4,7 @@
 #include "gtest/gtest.h"
 
 #include "aos/events/logging/buffer_encoder_param_test.h"
+#include "aos/testing/tmpdir.h"
 #include "aos/util/file.h"
 
 DECLARE_int32(lzma_threads);
@@ -62,8 +63,7 @@
 // corrupted.
 TEST_F(BufferEncoderBaseTest, CorruptedBuffer) {
   std::uniform_int_distribution<int> quantity_distribution(20, 60);
-  const char *const test_dir = CHECK_NOTNULL(getenv("TEST_TMPDIR"));
-  const std::string file_path = std::string(test_dir) + "/foo";
+  const std::string file_path = aos::testing::TestTmpDir() + "/foo";
 
   std::vector<std::vector<uint8_t>> encoded_buffers;
   {