diff --git a/tests/helpers/load-plugin-modules.mjs b/tests/helpers/load-plugin-modules.mjs
index cb3e5bf..58d9178 100644
--- a/tests/helpers/load-plugin-modules.mjs
+++ b/tests/helpers/load-plugin-modules.mjs
@@ -76,6 +76,7 @@ export async function bundleSource(entry, outputName, external = [], plugins = [
   return outfile;
 }
 
+let slideInsertionsModulePromise;
 let textUtilsModulePromise;
 let idleScheduleModulePromise;
 
@@ -637,3 +638,11 @@ export function loadDocxEmbedLoaderModule() {
   });
   return docxEmbedLoaderModulePromise;
 }
+
+export function loadSlideInsertionsModule() {
+  slideInsertionsModulePromise ??= bundleSource(
+    "src/SlideInsertions.ts",
+    "slide-insertions.cjs",
+  ).then((outfile) => require(outfile));
+  return slideInsertionsModulePromise;
+}
diff --git a/tests/slide-insertions.test.mjs b/tests/slide-insertions.test.mjs
new file mode 100644
index 0000000..feff5d1
--- /dev/null
+++ b/tests/slide-insertions.test.mjs
@@ -0,0 +1,67 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { loadSlideInsertionsModule } from "./helpers/load-plugin-modules.mjs";
+
+test("buildDuplicateSlideOrder builds correct order array", async () => {
+  const { buildDuplicateSlideOrder } = await loadSlideInsertionsModule();
+
+  // slideCount, sourceIndex, insertedIdx
+  // e.g., slides 0, 1, 2. We duplicate 1, inserting it at index 2.
+  // The slides were [0, 1, 2], so the new order should refer to old slides: [0, 1, 1, 2] -> 0 is old 0, 1 is old 1, 2 is old 1, 3 is old 2.
+  assert.deepEqual(buildDuplicateSlideOrder(4, 1, 2), [0, 1, 1, 2]);
+
+  // Duplicating the first slide (index 0) and inserting at index 1
+  assert.deepEqual(buildDuplicateSlideOrder(2, 0, 1), [0, 0]);
+
+  // Duplicating the last slide in a 3-slide deck (source=2, inserted at 3), total count will be 4
+  assert.deepEqual(buildDuplicateSlideOrder(4, 2, 3), [0, 1, 2, 2]);
+});
+
+test("countSlideTopLevelShapes returns correct number of top level shapes", async () => {
+  const { countSlideTopLevelShapes } = await loadSlideInsertionsModule();
+
+  const xml0 = `
+    <p:sld xmlns:p="http://schemas.openxmlformats.org/presentationml/2006/main">
+      <p:cSld>
+        <p:spTree>
+          <p:nvGrpSpPr><p:cNvPr id="1" name=""/><p:cNvGrpSpPr/><p:nvPr/></p:nvGrpSpPr>
+          <p:grpSpPr/>
+        </p:spTree>
+      </p:cSld>
+    </p:sld>
+  `;
+  assert.equal(countSlideTopLevelShapes(xml0, "ppt/slides/slide1.xml"), 0);
+
+  const xml2 = `
+    <p:sld xmlns:p="http://schemas.openxmlformats.org/presentationml/2006/main">
+      <p:cSld>
+        <p:spTree>
+          <p:nvGrpSpPr><p:cNvPr id="1" name=""/><p:cNvGrpSpPr/><p:nvPr/></p:nvGrpSpPr>
+          <p:grpSpPr/>
+          <p:sp><p:nvSpPr><p:cNvPr id="2" name="Shape 1"/></p:nvSpPr></p:sp>
+          <p:cxnSp><p:nvCxnSpPr><p:cNvPr id="3" name="Shape 2"/></p:nvCxnSpPr></p:cxnSp>
+        </p:spTree>
+      </p:cSld>
+    </p:sld>
+  `;
+  assert.equal(countSlideTopLevelShapes(xml2, "ppt/slides/slide2.xml"), 2);
+
+  const xmlWithGroups = `
+    <p:sld xmlns:p="http://schemas.openxmlformats.org/presentationml/2006/main">
+      <p:cSld>
+        <p:spTree>
+          <p:nvGrpSpPr><p:cNvPr id="1" name=""/><p:cNvGrpSpPr/><p:nvPr/></p:nvGrpSpPr>
+          <p:grpSpPr/>
+          <p:sp><p:nvSpPr><p:cNvPr id="2" name="Shape 1"/></p:nvSpPr></p:sp>
+          <p:grpSp>
+             <p:nvGrpSpPr><p:cNvPr id="3" name="Group 1"/></p:nvGrpSpPr>
+             <p:sp><p:nvSpPr><p:cNvPr id="4" name="Inner Shape 1"/></p:nvSpPr></p:sp>
+          </p:grpSp>
+          <p:pic><p:nvPicPr><p:cNvPr id="5" name="Pic 1"/></p:nvPicPr></p:pic>
+        </p:spTree>
+      </p:cSld>
+    </p:sld>
+  `;
+  // Expected to count <p:sp>, <p:grpSp>, and <p:pic> as top-level children of the spTree
+  assert.equal(countSlideTopLevelShapes(xmlWithGroups, "ppt/slides/slide3.xml"), 3);
+});