diff --git a/tests/HeapSnapshotManager.test.ts b/tests/HeapSnapshotManager.test.ts
index ee5cb259e..2bd4aca0e 100644
--- a/tests/HeapSnapshotManager.test.ts
+++ b/tests/HeapSnapshotManager.test.ts
@@ -5,12 +5,14 @@
  */
 
 import assert from 'node:assert';
-import {describe, it, afterEach} from 'node:test';
+import {join} from 'node:path';
+import {describe, it, after, afterEach} from 'node:test';
 
 import sinon from 'sinon';
 
 import {HeapSnapshotManager} from '../src/HeapSnapshotManager.js';
 import {DevTools} from '../src/third_party/index.js';
+import {stableIdSymbol} from '../src/utils/id.js';
 
 describe('HeapSnapshotManager', () => {
   afterEach(() => {
@@ -36,4 +38,187 @@ describe('HeapSnapshotManager', () => {
 
     sinon.assert.calledOnce(disposeSpy);
   });
+
+  describe('with the example fixture', () => {
+    const fixturePath = join(
+      process.cwd(),
+      'tests/fixtures/example.heapsnapshot',
+    );
+    const manager = new HeapSnapshotManager();
+
+    after(() => {
+      manager.dispose();
+    });
+
+    it('caches snapshots by resolved path', async () => {
+      const first = await manager.getSnapshot(fixturePath);
+      const second = await manager.getSnapshot(fixturePath);
+      const viaRelativePath = await manager.getSnapshot(
+        'tests/fixtures/example.heapsnapshot',
+      );
+
+      assert.strictEqual(second, first);
+      assert.strictEqual(viaRelativePath, first);
+    });
+
+    it('aggregates classes with totals and stable ids', async () => {
+      const data = await manager.getAggregates(fixturePath);
+      const aggregates = Object.values(data.aggregates);
+      assert.ok(aggregates.length > 0);
+
+      let objectCount = 0;
+      let totalSelfSize = 0;
+      const ids = new Set<number>();
+      for (const aggregate of aggregates) {
+        objectCount += aggregate.count;
+        totalSelfSize += aggregate.self;
+        const id = aggregate[stableIdSymbol];
+        assert.ok(typeof id === 'number' && id > 0);
+        ids.add(id);
+      }
+
+      assert.ok(data.objectCount > 0);
+      assert.ok(data.totalSelfSize > 0);
+      assert.strictEqual(data.objectCount, objectCount);
+      assert.strictEqual(data.totalSelfSize, totalSelfSize);
+      // Every class gets a distinct id.
+      assert.strictEqual(ids.size, aggregates.length);
+
+      const arrayAggregate = aggregates.find(
+        aggregate => aggregate.name === 'Array',
+      );
+      assert.ok(arrayAggregate);
+      assert.strictEqual(arrayAggregate.count, 8);
+    });
+
+    it('returns stable class ids that resolve back to class keys', async () => {
+      const first = await manager.getAggregates(fixturePath);
+      const second = await manager.getAggregates(fixturePath);
+
+      for (const [classKey, aggregate] of Object.entries(first.aggregates)) {
+        const id = aggregate[stableIdSymbol];
+        assert.ok(id);
+        const other = second.aggregates[classKey];
+        assert.ok(other);
+        assert.strictEqual(other[stableIdSymbol], id);
+        assert.strictEqual(
+          await manager.resolveClassKeyFromId(fixturePath, id),
+          classKey,
+        );
+        assert.strictEqual(
+          await manager.getOrCreateIdForClassKey(fixturePath, classKey),
+          id,
+        );
+      }
+    });
+
+    it('applies the objectsRetainedByContexts filter', async () => {
+      const unfiltered = await manager.getAggregates(fixturePath);
+      const filtered = await manager.getAggregates(
+        fixturePath,
+        'objectsRetainedByContexts',
+      );
+
+      assert.ok(filtered.objectCount > 0);
+      assert.ok(filtered.objectCount < unfiltered.objectCount);
+      assert.ok(
+        Object.values(filtered.aggregates).some(
+          aggregate => aggregate.name === 'Function',
+        ),
+      );
+    });
+
+    it('rejects attributedToSpecificNativeContext without an objectId', async () => {
+      await assert.rejects(
+        manager.getAggregates(fixturePath, 'attributedToSpecificNativeContext'),
+        {
+          message:
+            'objectId is required when filterName is attributedToSpecificNativeContext',
+        },
+      );
+    });
+
+    it('reports snapshot statistics', async () => {
+      const stats = await manager.getStats(fixturePath);
+
+      assert.strictEqual(stats.total, 1121496);
+      assert.strictEqual(stats.native.total + stats.v8heap.total, stats.total);
+      for (const value of [
+        stats.native.typedArrays,
+        stats.v8heap.code,
+        stats.v8heap.jsArrays,
+        stats.v8heap.strings,
+        stats.v8heap.system,
+      ]) {
+        assert.ok(typeof value === 'number' && value >= 0);
+      }
+    });
+
+    it('exposes static data once the snapshot is loaded', async () => {
+      const staticData = await manager.getStaticData(fixturePath);
+      assert.ok(staticData);
+      assert.strictEqual(staticData.nodeCount, 27466);
+      assert.strictEqual(staticData.rootNodeIndex, 0);
+      assert.strictEqual(staticData.maxJSObjectId, 54005);
+
+      const stats = await manager.getStats(fixturePath);
+      assert.strictEqual(staticData.totalSize, stats.total);
+    });
+
+    it('computes native context sizes', async () => {
+      const sizes = await manager.getNativeContextSizes(fixturePath);
+
+      assert.strictEqual(sizes.nativeContexts.length, 4);
+      for (const nativeContext of sizes.nativeContexts) {
+        assert.ok(nativeContext.nodeName.startsWith('system / NativeContext'));
+        assert.ok(nativeContext.selfSize > 0);
+        assert.ok(nativeContext.retainedSize > 0);
+        assert.ok(nativeContext.attributedSize > 0);
+      }
+      assert.ok(
+        sizes.nativeContexts.some(
+          nativeContext => nativeContext.nodeId === 7249,
+        ),
+      );
+      assert.ok(sizes.sharedSize > 0);
+      assert.ok(sizes.noAttributionSize > 0);
+    });
+  });
+
+  describe('snapshot lifecycle', () => {
+    it('tracks and disposes loaded snapshots', async () => {
+      const manager = new HeapSnapshotManager();
+      const fixturePath = join(
+        process.cwd(),
+        'tests/fixtures/heap-1.heapsnapshot',
+      );
+      try {
+        assert.strictEqual(manager.hasSnapshots(), false);
+
+        await manager.getSnapshot(fixturePath);
+        assert.strictEqual(manager.hasSnapshots(), true);
+
+        // disposeSnapshot resolves relative paths like getSnapshot does.
+        assert.strictEqual(
+          manager.disposeSnapshot('tests/fixtures/heap-1.heapsnapshot'),
+          true,
+        );
+        assert.strictEqual(manager.hasSnapshots(), false);
+        assert.strictEqual(manager.disposeSnapshot(fixturePath), false);
+      } finally {
+        manager.dispose();
+      }
+    });
+
+    it('rejects class key lookups for snapshots that are not loaded', async () => {
+      const manager = new HeapSnapshotManager();
+      await assert.rejects(
+        manager.getOrCreateIdForClassKey(
+          '/nonexistent/missing.heapsnapshot',
+          'Foo',
+        ),
+        /Snapshot not loaded/,
+      );
+    });
+  });
 });
diff --git a/tests/formatters/HeapSnapshotFormatter.test.ts b/tests/formatters/HeapSnapshotFormatter.test.ts
index 57d364356..334e3fda2 100644
--- a/tests/formatters/HeapSnapshotFormatter.test.ts
+++ b/tests/formatters/HeapSnapshotFormatter.test.ts
@@ -7,7 +7,11 @@
 import assert from 'node:assert';
 import {describe, it} from 'node:test';
 
-import {HeapSnapshotFormatter} from '../../src/formatters/HeapSnapshotFormatter.js';
+import {
+  HeapSnapshotFormatter,
+  isNodeLike,
+  isEdgeLike,
+} from '../../src/formatters/HeapSnapshotFormatter.js';
 import {DevTools} from '../../src/third_party/index.js';
 import {stableIdSymbol} from '../../src/utils/id.js';
 
@@ -78,6 +82,117 @@ describe('HeapSnapshotFormatter', () => {
     });
   });
 
+  describe('isNodeLike', () => {
+    it('returns true for objects with id and name', () => {
+      assert.strictEqual(isNodeLike({id: 1, name: 'NodeA'}), true);
+    });
+
+    it('returns true for a full node shape', () => {
+      assert.strictEqual(
+        isNodeLike({
+          id: 1,
+          name: 'NodeA',
+          distance: 0,
+          nodeIndex: 0,
+          retainedSize: 0,
+          selfSize: 0,
+          type: 'object',
+          canBeQueried: false,
+          detachedDOMTreeNode: false,
+          ignored: false,
+          isAddedNotRemoved: null,
+        }),
+        true,
+      );
+    });
+
+    it('returns false for null and undefined', () => {
+      assert.strictEqual(isNodeLike(null), false);
+      assert.strictEqual(isNodeLike(undefined), false);
+    });
+
+    it('returns false for primitives', () => {
+      assert.strictEqual(isNodeLike(42), false);
+      assert.strictEqual(isNodeLike('node'), false);
+    });
+
+    it('returns false for an empty object', () => {
+      assert.strictEqual(isNodeLike({}), false);
+    });
+
+    it('returns false when id or name is missing', () => {
+      assert.strictEqual(isNodeLike({id: 1}), false);
+      assert.strictEqual(isNodeLike({name: 'NodeA'}), false);
+    });
+
+    it('returns false for an edge shape', () => {
+      assert.strictEqual(
+        isNodeLike({
+          name: 'edge1',
+          type: 'property',
+          node: {id: 1, name: 'NodeA'},
+        }),
+        false,
+      );
+    });
+  });
+
+  describe('isEdgeLike', () => {
+    const validEdge = {
+      name: 'edge1',
+      type: 'property',
+      node: {id: 1, name: 'NodeA'},
+    };
+
+    it('returns true for objects with name, type and a node-like node', () => {
+      assert.strictEqual(isEdgeLike(validEdge), true);
+    });
+
+    it('returns false for null and undefined', () => {
+      assert.strictEqual(isEdgeLike(null), false);
+      assert.strictEqual(isEdgeLike(undefined), false);
+    });
+
+    it('returns false for an empty object', () => {
+      assert.strictEqual(isEdgeLike({}), false);
+    });
+
+    it('returns false when a top-level property is missing', () => {
+      assert.strictEqual(
+        isEdgeLike({type: validEdge.type, node: validEdge.node}),
+        false,
+      );
+      assert.strictEqual(
+        isEdgeLike({name: validEdge.name, node: validEdge.node}),
+        false,
+      );
+      assert.strictEqual(
+        isEdgeLike({name: validEdge.name, type: validEdge.type}),
+        false,
+      );
+    });
+
+    it('returns false when node is not an object', () => {
+      assert.strictEqual(isEdgeLike({...validEdge, node: null}), false);
+      assert.strictEqual(isEdgeLike({...validEdge, node: 42}), false);
+    });
+
+    it('returns false when node is missing id or name', () => {
+      assert.strictEqual(
+        isEdgeLike({...validEdge, node: {name: 'NodeA'}}),
+        false,
+      );
+      assert.strictEqual(isEdgeLike({...validEdge, node: {id: 1}}), false);
+    });
+
+    it('returns false for a node shape', () => {
+      assert.strictEqual(
+        isEdgeLike({id: 1, name: 'NodeA', type: 'object'}),
+        false,
+      );
+    });
+  });
+
   describe('formatNodes', () => {
     it('formats edges correctly', () => {
       const mockEdges = [
@@ -130,6 +245,50 @@ describe('HeapSnapshotFormatter', () => {
 
       assert.strictEqual(result, expected);
     });
+
+    it('formats nodes correctly', () => {
+      const mockNodes = [
+        {
+          id: 1,
+          name: 'NodeA',
+          distance: 2,
+          nodeIndex: 0,
+          retainedSize: 2048,
+          selfSize: 1024,
+          type: 'object',
+          canBeQueried: false,
+          detachedDOMTreeNode: false,
+          ignored: false,
+          isAddedNotRemoved: null,
+        },
+        {
+          id: 2,
+          name: 'NodeB',
+          distance: 3,
+          nodeIndex: 1,
+          retainedSize: 512,
+          selfSize: 256,
+          type: 'closure',
+          canBeQueried: false,
+          detachedDOMTreeNode: false,
+          ignored: false,
+          isAddedNotRemoved: null,
+        },
+      ];
+
+      const result = HeapSnapshotFormatter.formatNodes(mockNodes);
+      const expected = [
+        'nodeId,nodeName,type,distance,selfSize,retainedSize',
+        `1,NodeA,object,2,${formatBytesToKb(1024)},${formatBytesToKb(2048)}`,
+        `2,NodeB,closure,3,${formatBytesToKb(256)},${formatBytesToKb(512)}`,
+      ].join('\n');
+
+      assert.strictEqual(result, expected);
+    });
+
+    it('returns an empty string for an empty array', () => {
+      assert.strictEqual(HeapSnapshotFormatter.formatNodes([]), '');
+    });
   });
 
   describe('formatDiffSummary', () => {