Add system test checker

.kokoro/require-system-tests.cfg

@@ -0,0 +1,7 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Tell the trampoline which build file to use.
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/nodejs-docs-samples/.kokoro/require-system-tests.sh"
+}

.kokoro/require-system-tests.sh

@@ -0,0 +1,59 @@
+#!/bin/bash
+
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# CONFIGURATION
+CHECKED_PKG_NAME="@google-cloud/(\w|\\-)+"
+EXCLUSION_COMMENT="kokoro-allow-mock"
+
+# Get imports
+allImports=$(grep -sHoE "\W+${CHECKED_PKG_NAME}(.*${EXCLUSION_COMMENT})?" **/*.test.js --exclude=node_modules)
+sysImports=$(grep -sHoE "require\\(\W${CHECKED_PKG_NAME}(.*${EXCLUSION_COMMENT})?" **/*.test.js --exclude=node_modules)
+sysImports=$(echo $sysImports | sed s/require//g)
+
+# Ignore excluded imports
+allImports=$(echo $allImports | grep -v ${EXCLUSION_COMMENT}); 
+sysImports=$(echo $sysImports | grep -v ${EXCLUSION_COMMENT});
+
+# Remove filenames (but not directories)
+allImports=$(echo $allImports | awk -F '[/:]' '{ OFS="/"; if ($NF>2) { $(NF-2)=""; $(NF-3)=""; } print }'); # [[:space:]]
+sysImports=$(echo $sysImports | awk -F '[/:]' '{ OFS="/"; if ($NF>2) { $(NF-2)=""; $(NF-3)=""; } print }');
+
+# Remove excess whitespace + other cruft
+allImports=$(echo $allImports | sed -e "s/[^0-9a-zA-Z]*@/:@/g")
+sysImports=$(echo $sysImports | sed -e "s/[^0-9a-zA-Z]*@/:@/g")
+
+# Convert to library lists + dedupe
+allLibs=$(echo $allImports | egrep -s $CHECKED_PKG_NAME | sort | uniq)
+sysLibs=$(echo $sysImports | egrep -s $CHECKED_PKG_NAME | sort | uniq)
+
+# Remove whitelisted libraries
+for lib in "nodejs-repo-tools"
+do
+	allLibs=($(echo $allLibs | grep -v "$lib"))
+	sysLibs=($(echo $sysLibs | grep -v "$lib"))
+done
+
+# Check equality
+errCode=0
+for lib in $allLibs
+do
+	if ! echo $sysLibs | grep -q "$lib"; then
+		echo "No system tests (or missing $EXCLUSION_COMMENT comment): ${lib}"
+		errCode=1
+	fi
+done
+
+#exit $errCode