diff --git a/src/testRunner/unittests/tsbuild/amdModulesWithOut.ts b/src/testRunner/unittests/tsbuild/amdModulesWithOut.ts
index 19413d89989..c037c310043 100644
--- a/src/testRunner/unittests/tsbuild/amdModulesWithOut.ts
+++ b/src/testRunner/unittests/tsbuild/amdModulesWithOut.ts
@@ -72,7 +72,6 @@ namespace ts {
                     [outputFiles[project.lib][ext.buildinfo], outputFiles[project.lib][ext.js], outputFiles[project.lib][ext.dts]],
                     [outputFiles[project.app][ext.buildinfo], outputFiles[project.app][ext.js], outputFiles[project.app][ext.dts]]
                 ],
-                lastProjectOutput: outputFiles[project.app][ext.js],
                 initialBuild: {
                     modifyFs
                 },
@@ -217,7 +216,6 @@ ${internal} export enum internalEnum { a, b, c }`);
                         [libOutputFile[ext.buildinfo], libOutputFile[ext.js], libOutputFile[ext.dts]],
                         [outputFiles[project.app][ext.buildinfo], outputFiles[project.app][ext.js], outputFiles[project.app][ext.dts]]
                     ],
-                    lastProjectOutput: outputFiles[project.app][ext.js],
                     initialBuild: {
                         modifyFs,
                         expectedDiagnostics: [
diff --git a/src/testRunner/unittests/tsbuild/emitDeclarationOnly.ts b/src/testRunner/unittests/tsbuild/emitDeclarationOnly.ts
index 73dc36c1a0a..e9ce4b46024 100644
--- a/src/testRunner/unittests/tsbuild/emitDeclarationOnly.ts
+++ b/src/testRunner/unittests/tsbuild/emitDeclarationOnly.ts
@@ -17,7 +17,6 @@ namespace ts {
                 tick,
                 proj: "emitDeclarationOnly",
                 rootNames: ["/src"],
-                lastProjectOutput: `/src/lib/index.d.ts`,
                 initialBuild: {
                     modifyFs: disableMap ?
                         (fs => replaceText(fs, "/src/tsconfig.json", `"declarationMap": true,`, "")) :
@@ -50,7 +49,6 @@ namespace ts {
             tick,
             proj: "emitDeclarationOnly",
             rootNames: ["/src"],
-            lastProjectOutput: `/src/lib/a.d.ts`,
             initialBuild: {
                 modifyFs: fs => {
                     fs.rimrafSync("/src/src/index.ts");
diff --git a/src/testRunner/unittests/tsbuild/helpers.ts b/src/testRunner/unittests/tsbuild/helpers.ts
index 5d656589b71..b204daef0fb 100644
--- a/src/testRunner/unittests/tsbuild/helpers.ts
+++ b/src/testRunner/unittests/tsbuild/helpers.ts
@@ -312,7 +312,6 @@ Mismatch Actual(path, actual, expected): ${JSON.stringify(arrayFrom(mapDefinedIt
         proj: string;
         rootNames: ReadonlyArray<string>;
         expectedBuildInfoFilesForSectionBaselines?: ReadonlyArray<BuildInfoSectionBaselineFiles>;
-        lastProjectOutput: string;
         initialBuild: BuildState;
         incrementalDtsChangedBuild?: BuildState;
         incrementalDtsUnchangedBuild?: BuildState;
@@ -324,7 +323,7 @@ Mismatch Actual(path, actual, expected): ${JSON.stringify(arrayFrom(mapDefinedIt
 
     export function verifyTsbuildOutput({
         scenario, projFs, time, tick, proj, rootNames, baselineOnly, verifyDiagnostics,
-        baselineSourceMap, expectedBuildInfoFilesForSectionBaselines, lastProjectOutput,
+        baselineSourceMap, expectedBuildInfoFilesForSectionBaselines,
         initialBuild, incrementalDtsChangedBuild, incrementalDtsUnchangedBuild, incrementalHeaderChangedBuild
     }: VerifyTsBuildInput) {
         describe(`tsc --b ${proj}:: ${scenario}`, () => {
@@ -332,6 +331,7 @@ Mismatch Actual(path, actual, expected): ${JSON.stringify(arrayFrom(mapDefinedIt
             let actualReadFileMap: Map<number>;
             let firstBuildTime: number;
             let host: fakes.SolutionBuilderHost;
+            let initialWrittenFiles: Map<true>;
             before(() => {
                 const result = build({
                     fs: projFs().shadow(),
@@ -341,13 +341,14 @@ Mismatch Actual(path, actual, expected): ${JSON.stringify(arrayFrom(mapDefinedIt
                     expectedBuildInfoFilesForSectionBaselines,
                     modifyFs: initialBuild.modifyFs,
                 });
-                ({ fs, actualReadFileMap, host } = result);
+                ({ fs, actualReadFileMap, host, writtenFiles: initialWrittenFiles } = result);
                 firstBuildTime = time();
             });
             after(() => {
                 fs = undefined!;
                 actualReadFileMap = undefined!;
                 host = undefined!;
+                initialWrittenFiles = undefined!;
             });
             describe("initialBuild", () => {
                 if (!baselineOnly || verifyDiagnostics) {
@@ -373,6 +374,7 @@ Mismatch Actual(path, actual, expected): ${JSON.stringify(arrayFrom(mapDefinedIt
                     let beforeBuildTime: number;
                     let afterBuildTime: number;
                     before(() => {
+                        const lastProjectOutput = last(arrayFrom(initialWrittenFiles.keys()));
                         beforeBuildTime = fs.statSync(lastProjectOutput).mtimeMs;
                         tick();
                         newFs = fs.shadow();
diff --git a/src/testRunner/unittests/tsbuild/inferredTypeFromTransitiveModule.ts b/src/testRunner/unittests/tsbuild/inferredTypeFromTransitiveModule.ts
index 81822df5652..92762dfd49d 100644
--- a/src/testRunner/unittests/tsbuild/inferredTypeFromTransitiveModule.ts
+++ b/src/testRunner/unittests/tsbuild/inferredTypeFromTransitiveModule.ts
@@ -16,7 +16,6 @@ namespace ts {
             tick,
             proj: "inferredTypeFromTransitiveModule",
             rootNames: ["/src"],
-            lastProjectOutput: `/src/obj/index.js`,
             initialBuild: {
                 modifyFs: noop,
                 expectedDiagnostics: [
diff --git a/src/testRunner/unittests/tsbuild/lateBoundSymbol.ts b/src/testRunner/unittests/tsbuild/lateBoundSymbol.ts
index 72c7c0b80e2..02224b3fa88 100644
--- a/src/testRunner/unittests/tsbuild/lateBoundSymbol.ts
+++ b/src/testRunner/unittests/tsbuild/lateBoundSymbol.ts
@@ -16,7 +16,6 @@ namespace ts {
             tick,
             proj: "lateBoundSymbol",
             rootNames: ["/src/tsconfig.json"],
-            lastProjectOutput: "/src/src/main.js",
             initialBuild: {
                 modifyFs: noop,
                 expectedDiagnostics: [
diff --git a/src/testRunner/unittests/tsbuild/moduleSpecifiers.ts b/src/testRunner/unittests/tsbuild/moduleSpecifiers.ts
index c6737b9d2f7..86328788a3b 100644
--- a/src/testRunner/unittests/tsbuild/moduleSpecifiers.ts
+++ b/src/testRunner/unittests/tsbuild/moduleSpecifiers.ts
@@ -96,7 +96,6 @@ namespace ts {
             tick,
             proj: "moduleSpecifiers",
             rootNames: ["/"],
-            lastProjectOutput: `/src/lib/index.d.ts`,
             initialBuild: {
                 modifyFs: noop,
             },
diff --git a/src/testRunner/unittests/tsbuild/outFile.ts b/src/testRunner/unittests/tsbuild/outFile.ts
index dfc6d4cc327..db8d0873e76 100644
--- a/src/testRunner/unittests/tsbuild/outFile.ts
+++ b/src/testRunner/unittests/tsbuild/outFile.ts
@@ -280,7 +280,6 @@ namespace ts {
                 rootNames: ["/src/third"],
                 baselineSourceMap: true,
                 expectedBuildInfoFilesForSectionBaselines: expectedBuildInfoFilesForSectionBaselines || expectedTsbuildInfoFileNames,
-                lastProjectOutput: outputFiles[project.third][ext.js],
                 initialBuild: {
                     modifyFs,
                     expectedDiagnostics: initialExpectedDiagnostics,
diff --git a/src/testRunner/unittests/tsbuild/sample.ts b/src/testRunner/unittests/tsbuild/sample.ts
index 7e3f12bc4e7..d95ba5e514a 100644
--- a/src/testRunner/unittests/tsbuild/sample.ts
+++ b/src/testRunner/unittests/tsbuild/sample.ts
@@ -613,7 +613,6 @@ export class cNew {}`);
                 proj: "sample1",
                 rootNames: ["/src/tests"],
                 baselineSourceMap: true,
-                lastProjectOutput: "/src/tests/index.js",
                 initialBuild,
                 incrementalDtsChangedBuild: {
                     modifyFs: fs => appendText(fs, "/src/core/index.ts", `
@@ -703,7 +702,6 @@ class someClass { }`),
                 proj: "sample1",
                 rootNames: ["/src/tests"],
                 baselineSourceMap: true,
-                lastProjectOutput: "/src/tests/index.js",
                 initialBuild,
                 incrementalDtsChangedBuild: {
                     modifyFs: fs => replaceText(fs, "/src/logic/tsconfig.json", `"declaration": true,`, `"declaration": true,
@@ -751,7 +749,6 @@ class someClass { }`),
                 proj: "sample1",
                 rootNames: ["/src/tests"],
                 baselineSourceMap: true,
-                lastProjectOutput: "/src/tests/index.js",
                 initialBuild: {
                     modifyFs: fs => replaceText(fs, "/src/logic/tsconfig.json", `"composite": true,`, `"composite": true,
         "tsBuildInfoFile": "ownFile.tsbuildinfo",`),
@@ -791,7 +788,6 @@ class someClass { }`),
                 tick,
                 proj: "sample1",
                 rootNames: ["/src/core"],
-                lastProjectOutput: "/src/core/index.js",
                 initialBuild: {
                     modifyFs: fs => fs.writeFileSync("/src/core/tsconfig.json", `{
     "compilerOptions": {
@@ -824,7 +820,6 @@ class someClass { }`),
                 tick,
                 proj: "sample1",
                 rootNames: ["/src/core"],
-                lastProjectOutput: "/src/core/index.js",
                 initialBuild: {
                     modifyFs: fs => {
                         fs.writeFileSync("/lib/lib.esnext.full.d.ts", `/// <reference no-default-lib="true"/>
@@ -866,7 +861,6 @@ class someClass { }`),
                 tick,
                 proj: "sample1",
                 rootNames: ["/src/core"],
-                lastProjectOutput: "/src/core/index.js",
                 initialBuild: {
                     modifyFs: fs => fs.writeFileSync("/src/core/tsconfig.json", `{
     "compilerOptions": {
@@ -899,7 +893,6 @@ class someClass { }`),
                 tick,
                 proj: "sample1",
                 rootNames: ["/src/tests"],
-                lastProjectOutput: "/src/tests/index.js",
                 initialBuild: {
                     modifyFs: fs => fs.writeFileSync("/src/tests/tsconfig.json", `{
     "references": [