diff --git a/test/report.test.js b/test/report.test.js
new file mode 100644
index 0000000..8319ec9
--- /dev/null
+++ b/test/report.test.js
@@ -0,0 +1,116 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import {
+  createSummary,
+  formatJsonReport,
+  formatTextReport,
+} from "../src/report.js";
+
+const now = Date.UTC(2026, 0, 15, 12);
+
+function cache(overrides = {}) {
+  return {
+    relativePath: "app/node_modules/.cache",
+    type: "node",
+    bytes: 2048,
+    files: 3,
+    modifiedAtMs: now - 2 * 24 * 60 * 60_000,
+    ...overrides,
+  };
+}
+
+test("creates aggregate summaries for report results", () => {
+  assert.deepEqual(createSummary([cache(), cache({ bytes: 512, files: 1 })]), {
+    directories: 2,
+    files: 4,
+    bytes: 2560,
+  });
+});
+
+test("formats dry-run text reports with cache rows and warnings", () => {
+  const output = formatTextReport({
+    root: "/workspace",
+    caches: [cache()],
+    warnings: ["/workspace/locked: EACCES"],
+    apply: false,
+    now,
+  });
+
+  assert.match(output, /Root: \/workspace/);
+  assert.match(output, /Matched 1 cache directories, 3 files, 2.00 KB\./);
+  assert.match(output, /TYPE\s+SIZE\s+AGE\s+FILES\s+PATH/);
+  assert.match(output, /node\s+2.00 KB\s+2d\s+3\s+app\/node_modules\/\.cache/);
+  assert.match(output, /Dry run only\. Add --apply to remove/);
+  assert.match(output, /Warnings: 1/);
+  assert.match(output, /- \/workspace\/locked: EACCES/);
+});
+
+test("formats apply reports with reclaimed bytes and failed removals", () => {
+  const output = formatTextReport({
+    root: "/workspace",
+    caches: [cache(), cache({ relativePath: "service/.pytest_cache" })],
+    warnings: [],
+    apply: true,
+    removalResults: [
+      { ...cache(), status: "removed" },
+      {
+        ...cache({ relativePath: "service/.pytest_cache", bytes: 4096 }),
+        status: "failed",
+        error: "permission denied",
+      },
+    ],
+    now,
+  });
+
+  assert.match(output, /Removed 1 cache directories and reclaimed 2.00 KB\./);
+  assert.match(output, /Failed: service\/\.pytest_cache: permission denied/);
+  assert.doesNotMatch(output, /Dry run only/);
+});
+
+test("formats stable JSON reports for scripts", () => {
+  const output = formatJsonReport({
+    root: "/workspace",
+    caches: [cache()],
+    warnings: ["scan warning"],
+    apply: true,
+    removalResults: [
+      { ...cache(), status: "removed" },
+      {
+        ...cache({ relativePath: "service/.pytest_cache" }),
+        status: "failed",
+        error: "permission denied",
+      },
+    ],
+  });
+
+  assert.deepEqual(JSON.parse(output), {
+    root: "/workspace",
+    mode: "apply",
+    summary: {
+      directories: 1,
+      files: 3,
+      bytes: 2048,
+    },
+    caches: [
+      {
+        path: "app/node_modules/.cache",
+        type: "node",
+        bytes: 2048,
+        files: 3,
+        modifiedAt: new Date(now - 2 * 24 * 60 * 60_000).toISOString(),
+      },
+    ],
+    removals: [
+      {
+        path: "app/node_modules/.cache",
+        status: "removed",
+      },
+      {
+        path: "service/.pytest_cache",
+        status: "failed",
+        error: "permission denied",
+      },
+    ],
+    warnings: ["scan warning"],
+  });
+});