Add tests for heapviz tool.

.github/workflows/heapviz_test.yml

@@ -0,0 +1,32 @@
+---
+name: Heapviz tool tests
+on:
+  push:
+    paths:
+      - 'tools/heapviz/**'
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+jobs:
+  cbor_test:
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Check heapviz tool
+        uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --manifest-path tool/heapviz/Cargo.toml
+
+      - name: Unit testing of heapviz tool (debug mode)
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --manifest-path tool/heapviz/Cargo.toml
+
+      - name: Unit testing of heapviz tool (release mode)
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --manifest-path tool/heapviz/Cargo.toml --release