tools/helper: Streamline return types

These functions can already return exceptions, so make better use of
them for reporting failures.

Change-Id: I572e9e3ee44bbd5add601f3246bb4f95cb9308bf
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/tools/test/tools_updater_unittest.cpp b/tools/test/tools_updater_unittest.cpp
index 60cc077..40b6798 100644
--- a/tools/test/tools_updater_unittest.cpp
+++ b/tools/test/tools_updater_unittest.cpp
@@ -210,9 +210,9 @@
                  ToolException);
 }
 
-TEST_F(UpdateHandlerTest, ReadVersionReturnsEmptyIfPollingFails)
+TEST_F(UpdateHandlerTest, ReadVersionReturnsErrorIfPollingFails)
 {
-    /* It can return an empty result, when polling fails. */
+    /* It can throw an error, when polling fails. */
     EXPECT_CALL(blobMock, openBlob(ipmi_flash::biosVersionBlobId, _))
         .WillOnce(Return(session));
     ipmiblob::StatResponse readVersionResponse = {};
@@ -220,7 +220,8 @@
     EXPECT_CALL(blobMock, getStat(TypedEq<std::uint16_t>(session)))
         .WillOnce(Return(readVersionResponse));
     EXPECT_CALL(blobMock, closeBlob(session)).WillOnce(Return());
-    EXPECT_THAT(updater.readVersion(ipmi_flash::biosVersionBlobId), IsEmpty());
+    EXPECT_THROW(updater.readVersion(ipmi_flash::biosVersionBlobId),
+                 ToolException);
 }
 
 TEST_F(UpdateHandlerTest, ReadVersionCovertsOpenBlobExceptionToToolException)