diff --git a/.circleci/config.yml b/.circleci/config.yml
index da54155fc57..3c11553785e 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -3,48 +3,55 @@ workflows:
   version: 2
   tests:
     jobs: &workflow_jobs
+      - node4:
+          filters:
+            tags:
+              only: /.*/
       - node6:
-          filters: &all_commits
+          filters:
             tags:
               only: /.*/
       - node8:
-          filters: *all_commits
+          filters:
+            tags:
+              only: /.*/
+      - node9:
+          filters:
+            tags:
+              only: /.*/
       - node10:
-          filters: *all_commits
+          filters:
+            tags:
+              only: /.*/
       - lint:
           requires:
+            - node4
             - node6
             - node8
+            - node9
             - node10
-          filters: *all_commits
+          filters:
+            tags:
+              only: /.*/
       - docs:
           requires:
+            - node4
             - node6
             - node8
+            - node9
             - node10
-          filters: *all_commits
-      - system_tests:
-          requires:
-            - lint
-            - docs
-          filters: &master_and_releases
-            branches:
-              only: master
-            tags: &releases
-              only: '/^v[\d.]+$/'
-      - sample_tests:
+          filters:
+            tags:
+              only: /.*/
+      - publish_npm:
           requires:
             - lint
             - docs
-          filters: *master_and_releases
-      - publish_npm:
-          requires:
-            - system_tests
-            - sample_tests
           filters:
             branches:
               ignore: /.*/
-            tags: *releases
+            tags:
+              only: '/^v[\d.]+$/'
   nightly:
     triggers:
       - schedule:
@@ -54,25 +61,48 @@ workflows:
               only: master
     jobs: *workflow_jobs
 jobs:
-  node6:
+  node4:
     docker:
-      - image: 'node:6'
+      - image: 'node:4'
         user: node
     steps: &unit_tests_steps
       - checkout
-      - run: &npm_install_and_link
-          name: Install and link the module
-          command: |-
-            mkdir -p /home/node/.npm-global
-            ./.circleci/npm-install-retry.js
-          environment:
-            NPM_CONFIG_PREFIX: /home/node/.npm-global
-      - run: npm test
+      - run: &remove_package_lock
+          name: Remove package-lock.json if needed.
+          command: |
+            WORKFLOW_NAME=`python .circleci/get_workflow_name.py`
+            echo "Workflow name: $WORKFLOW_NAME"
+            if [ "$WORKFLOW_NAME" = "nightly" ]; then
+              echo "Nightly build detected, removing package-lock.json."
+              rm -f package-lock.json samples/package-lock.json
+            else
+              echo "Not a nightly build, skipping this step."
+            fi
+      - run:
+          name: Install modules and dependencies.
+          command: npm install
+      - run:
+          name: Run unit tests.
+          command: npm run test-only
+      - run:
+          name: Submit coverage data to codecov.
+          command: node_modules/.bin/codecov
+          when: always
+  node6:
+    docker:
+      - image: 'node:6'
+        user: node
+    steps: *unit_tests_steps
   node8:
     docker:
       - image: 'node:8'
         user: node
     steps: *unit_tests_steps
+  node9:
+    docker:
+      - image: 'node:9'
+        user: node
+    steps: *unit_tests_steps
   node10:
     docker:
       - image: 'node:10'
@@ -84,18 +114,18 @@ jobs:
         user: node
     steps:
       - checkout
-      - run: *npm_install_and_link
-      - run: &samples_npm_install_and_link
-          name: Link the module being tested to the samples.
+      - run: *remove_package_lock
+      - run:
+          name: Install modules and dependencies.
           command: |
-            cd samples/
-            npm link ../
-            ./../.circleci/npm-install-retry.js
+            mkdir -p /home/node/.npm-global
+            npm install
+            npm link
           environment:
             NPM_CONFIG_PREFIX: /home/node/.npm-global
       - run:
           name: Run linting.
-          command: npm run lint
+          command: npm run check
           environment:
             NPM_CONFIG_PREFIX: /home/node/.npm-global
   docs:
@@ -104,75 +134,25 @@ jobs:
         user: node
     steps:
       - checkout
-      - run: *npm_install_and_link
-      - run: npm run docs
-  sample_tests:
-    docker:
-      - image: 'node:8'
-        user: node
-    steps:
-      - checkout
-      - run:
-          name: Decrypt credentials.
-          command: |
-            if ! [[ -z "${SYSTEM_TESTS_ENCRYPTION_KEY}" ]]; then
-              openssl aes-256-cbc -d -in .circleci/key.json.enc \
-                -out .circleci/key.json \
-                -k "${SYSTEM_TESTS_ENCRYPTION_KEY}"
-            fi
-      - run: *npm_install_and_link
-      - run: *samples_npm_install_and_link
+      - run: *remove_package_lock
       - run:
-          name: Run sample tests.
-          command: npm run samples-test
-          environment:
-            GCLOUD_PROJECT: long-door-651
-            GOOGLE_APPLICATION_CREDENTIALS: /home/node/samples/.circleci/key.json
-            NPM_CONFIG_PREFIX: /home/node/.npm-global
+          name: Install modules and dependencies.
+          command: npm install
       - run:
-          name: Remove unencrypted key.
-          command: |
-            if ! [[ -z "${SYSTEM_TESTS_ENCRYPTION_KEY}" ]]; then
-              rm .circleci/key.json
-            fi
-          when: always
-    working_directory: /home/node/samples/
-  system_tests:
+          name: Build documentation.
+          command: npm run docs
+  publish_npm:
     docker:
       - image: 'node:8'
         user: node
     steps:
       - checkout
       - run:
-          name: Decrypt credentials.
-          command: |
-            if ! [[ -z "${SYSTEM_TESTS_ENCRYPTION_KEY}" ]]; then
-              for encrypted_key in .circleci/*.json.enc; do
-                openssl aes-256-cbc -d -in $encrypted_key \
-                  -out $(echo $encrypted_key | sed 's/\.enc//') \
-                  -k "${SYSTEM_TESTS_ENCRYPTION_KEY}"
-              done
-            fi
-      - run: *npm_install_and_link
+          name: Set NPM authentication.
+          command: 'echo "//registry.npmjs.org/:_authToken=${NPM_TOKEN}" > ~/.npmrc'
       - run:
-          name: Run system tests.
-          command: npm run system-test
-          environment:
-            GCLOUD_PROJECT: long-door-651
-            GOOGLE_APPLICATION_CREDENTIALS: .circleci/key.json
+          name: Install dependencies
+          command: npm install --unsafe-perm
       - run:
-          name: Remove unencrypted key.
-          command: |
-            if ! [[ -z "${SYSTEM_TESTS_ENCRYPTION_KEY}" ]]; then
-              rm .circleci/*.json
-            fi
-          when: always
-  publish_npm:
-    docker:
-      - image: 'node:8'
-        user: node
-    steps:
-      - checkout
-      - run: ./.circleci/npm-install-retry.js
-      - run: echo "//registry.npmjs.org/:_authToken=${NPM_TOKEN}" > ~/.npmrc
-      - run: npm publish --access=public
+          name: Publish the module to npm.
+          command: npm publish