src: fix the base case in the heap profiler JSON generation

In the base case, the last node needs to have an empty array with
no childrens, this commit handles that by creating an empty array for
it.

Fixes: #124
Signed-off-by: Juan José Arboleda <soyjuanarbol@gmail.com>

src/nsolid/nsolid_heap_snapshot.cc

@@ -97,8 +97,10 @@ nlohmann::ordered_json build_sampling_heap_profile_node(
   result["id"] = node->node_id;
 
   // Add children if there are any
-  if (node->children.empty())
+  if (node->children.empty()) {
+    result["children"] = nlohmann::ordered_json::array();
     return result;
+  }
 
   // Recursively build children
   nlohmann::ordered_json children;

test/parallel/test-nsolid-heap-sampling-stream.js

@@ -102,10 +102,45 @@ const {
 {
   let profile = '';
   const stream = nsolid.heapSamplingStream(0, 1200);
+  // Do some allocations to make sure we have some data to sample
+  const arr = [];
+  for (let i = 0; i < 1000; i++) {
+    arr.push(new Array(1000));
+  }
   stream.on('data', (data) => {
     profile += data;
   });
   stream.on('end', common.mustCall(() => {
     assert(JSON.parse(profile));
+    testProfileSchema(JSON.parse(profile));
   }));
 }
+
+function testProfileSchema (profile) {
+  // Basic object schema test
+  assert(profile.head);
+  assert(profile.samples);
+
+  testCallFrame(profile.head);
+
+  // Recursive schema test per sample callframe
+  function testCallFrame (head) {
+    assert(Number.isInteger(head.callFrame.columnNumber));
+    assert(Number.isInteger(head.callFrame.lineNumber));
+    assert(Number.isInteger(head.selfSize));
+    assert(Number.isInteger(head.callFrame.scriptId));
+    assert(Number.isInteger(head.id));
+    assert(head.callFrame.functionName === '' ||
+           typeof head.callFrame.functionName === 'string');
+    assert(head.callFrame.url === '' || typeof head.callFrame.url === 'string');
+    assert(Array.isArray(head.children));
+    testChildren(head.children);
+  }
+
+  // Recursive children schema test
+  function testChildren (children) {
+    let isTestDone = children.length === 0;
+    if (!isTestDone) return testCallFrame(children[0]);
+    assert(isTestDone);
+  }
+}