kokoro: Check go tool unit tests

Change-Id: I9d3b34427fea524364480c1972f740213b3701c5
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86523
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

infra/kokoro/linux/docker.sh

@@ -75,7 +75,7 @@ CLONE_SRC_DIR="$(pwd)"
 . /bin/using.sh # Declare the bash `using` function for configuring toolchains.
 
 using depot_tools
-using go-1.14.4      # Speeds up ./tools/lint
+using go-1.18
 using doxygen-1.8.18
 
 status "Creating source directory '${SRC_DIR}' and build directory '${BUILD_DIR}'"
@@ -137,6 +137,13 @@ if [ "$BUILD_SYSTEM" == "cmake" ]; then
         export UBSAN_OPTIONS=print_stacktrace=1:halt_on_error=1
     fi
 
+    status "Running go tool unittests"
+    show_cmds
+        pushd tools/src
+            go test ./...
+        popd
+    hide_cmds
+
     cd ${BUILD_DIR}
 
     status "Running Doxygen"