diff --git a/.changeset/beige-timers-juggle.md b/.changeset/beige-timers-juggle.md
new file mode 100644
index 000000000..bb55a0e97
--- /dev/null
+++ b/.changeset/beige-timers-juggle.md
@@ -0,0 +1,5 @@
+---
+'@web/test-runner-junit-reporter': minor
+---
+
+Update result format to match JUnit Schema definitions
diff --git a/packages/test-runner-junit-reporter/src/junitReporter.ts b/packages/test-runner-junit-reporter/src/junitReporter.ts
index 7ba8d5b79..96b3f3dd3 100644
--- a/packages/test-runner-junit-reporter/src/junitReporter.ts
+++ b/packages/test-runner-junit-reporter/src/junitReporter.ts
@@ -31,7 +31,6 @@ interface TestCaseXMLAttributes {
   _attr: {
     name: string;
     time: number;
-    file: string;
     line?: string;
     classname: string;
   };
@@ -62,7 +61,8 @@ interface TestSuiteXMLAttributes {
     skipped: number;
     errors: number;
     failures: number;
-    time: number;
+    time: string;
+    file: string;
   };
 }
 
@@ -120,8 +120,6 @@ const getTestName: TestMetaGetter = test => test.name;
 
 const getSuiteName: TestMetaGetter = test => test.suiteName;
 
-const getTestFile: TestMetaGetter = test => test.testFile;
-
 const getTestDurationInSeconds = ({ duration }: TestResult): number =>
   (typeof duration === 'undefined' ? 0 : duration) / 1000;
 
@@ -161,18 +159,13 @@ function testFailureXMLElement(test: TestResultWithMetadata): TestFailureXMLElem
  * Makes attributes for a `<testcase>` element
  * @param test Test Result
  */
-function testCaseXMLAttributes(
-  test: TestResultWithMetadata,
-  rootDir: string,
-): TestCaseXMLAttributes {
+function testCaseXMLAttributes(test: TestResultWithMetadata): TestCaseXMLAttributes {
   const name = getTestName(test);
 
   const time = getTestDurationInSeconds(test);
 
   const classname = getSuiteName(test);
 
-  const file = getTestFile(test).replace(`${rootDir}${path.sep}`, '');
-
   const [, line] = stripXMLInvalidChars(test.error?.stack ?? '').match(/(\d+):\d+/m) ?? [];
 
   return {
@@ -180,7 +173,6 @@ function testCaseXMLAttributes(
       name,
       time,
       classname,
-      file,
       ...(!!line && { line }),
     },
   };
@@ -189,8 +181,8 @@ function testCaseXMLAttributes(
 /**
  * Makes a `<testcase>` element
  */
-function testCaseXMLElement(test: TestResultWithMetadata, rootDir: string): TestCaseXMLElement {
-  const attributes = testCaseXMLAttributes(test, rootDir);
+function testCaseXMLElement(test: TestResultWithMetadata): TestCaseXMLElement {
+  const attributes = testCaseXMLAttributes(test);
 
   // prettier-ignore
   if (isSkippedTest(test))
@@ -211,6 +203,8 @@ function testSuiteXMLAttributes(
   name: string,
   id: number,
   results: TestResultWithMetadata[],
+  testFile: string,
+  rootDir: string,
 ): TestSuiteXMLAttributes {
   const tests = results.length;
 
@@ -220,7 +214,9 @@ function testSuiteXMLAttributes(
 
   const failures = results.filter(isFailedTest).length;
 
-  const time = results.reduce(addSuiteTime, 0);
+  const time = results.reduce(addSuiteTime, 0).toFixed(3);
+
+  const file = testFile.replace(`${rootDir}${path.sep}`, '');
 
   return {
     _attr: {
@@ -231,6 +227,7 @@ function testSuiteXMLAttributes(
       errors,
       failures,
       time,
+      file,
     },
   };
 }
@@ -303,11 +300,11 @@ function getTestRunXML({
 
     const launcherType = browser.type ?? '';
 
-    const attributes = testSuiteXMLAttributes(name, testRun, tests);
+    const attributes = testSuiteXMLAttributes(name, testRun, tests, testFile, rootDir);
 
     const properties = testSuitePropertiesXMLElement(testFile, browserName, launcherType, rootDir);
 
-    const testcases = tests.map(t => testCaseXMLElement(t, rootDir));
+    const testcases = tests.map(testCaseXMLElement);
 
     const systemOut = !reportLogs ? [] : tests.flatMap(escapeLogs).map(x => ({ 'system-out': x }));
 
diff --git a/packages/test-runner-junit-reporter/test/fixtures/multiple/expected.xml b/packages/test-runner-junit-reporter/test/fixtures/multiple/expected.xml
index 88dd3f7a4..6e4ce1472 100644
--- a/packages/test-runner-junit-reporter/test/fixtures/multiple/expected.xml
+++ b/packages/test-runner-junit-reporter/test/fixtures/multiple/expected.xml
@@ -1,28 +1,28 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuites>
-  <testsuite name="Chrome_puppeteer_/packages/test-runner-junit-reporter/test/fixtures/multiple/nested-test.js" id="0" tests="1" skipped="0" errors="0" failures="0" time="0.001">
+  <testsuite name="Chrome_puppeteer_/packages/test-runner-junit-reporter/test/fixtures/multiple/nested-test.js" id="0" tests="1" skipped="0" errors="0" failures="0" time="0.001" file="packages/test-runner-junit-reporter/test/fixtures/multiple/nested-test.js">
     <properties>
       <property name="test.fileName" value="packages/test-runner-junit-reporter/test/fixtures/multiple/nested-test.js"/>
       <property name="browser.name" value="Chrome"/>
       <property name="browser.launcher" value="puppeteer"/>
     </properties>
-    <testcase name="is equivalent to map (f.g) f a" time="<<computed>>" classname="given a functor f and a function a -&gt; b map f map g f a" file="packages/test-runner-junit-reporter/test/fixtures/multiple/nested-test.js"/>
+    <testcase name="is equivalent to map (f.g) f a" time="<<computed>>" classname="given a functor f and a function a -&gt; b map f map g f a"/>
   </testsuite>
-  <testsuite name="Chrome_puppeteer_/packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js" id="0" tests="5" skipped="1" errors="1" failures="1" time="0.001">
+  <testsuite name="Chrome_puppeteer_/packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js" id="0" tests="5" skipped="1" errors="1" failures="1" time="0.001" file="packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js">
     <properties>
       <property name="test.fileName" value="packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js"/>
       <property name="browser.name" value="Chrome"/>
       <property name="browser.launcher" value="puppeteer"/>
     </properties>
-    <testcase name="under addition" time="0.001" classname="real numbers forming a monoid" file="packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js"/>
-    <testcase name="null hypothesis" time="0.001" classname="off-by-one boolean logic errors" file="packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js"/>
-    <testcase name="asserts error" time="0.001" classname="off-by-one boolean logic errors" file="packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js" line="15">
+    <testcase name="under addition" time="0.001" classname="real numbers forming a monoid"/>
+    <testcase name="null hypothesis" time="0.001" classname="off-by-one boolean logic errors"/>
+    <testcase name="asserts error" time="0.001" classname="off-by-one boolean logic errors" line="15">
       <failure message="expected false to be true" type="AssertionError"><![CDATA[AssertionError: expected false to be true
   at o.<anonymous> (packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js:15:29)]]></failure>
     </testcase>
-    <testcase name="tbd: confirm true positive" time="0" classname="off-by-one boolean logic errors" file="packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js">
+    <testcase name="tbd: confirm true positive" time="0" classname="off-by-one boolean logic errors">
       <skipped/>
     </testcase>
-    <testcase name="reports logs to JUnit" time="0.001" classname="logging during a test" file="packages/test-runner-junit-reporter/test/fixtures/multiple/simple-test.js"/>
+    <testcase name="reports logs to JUnit" time="0.001" classname="logging during a test"/>
   </testsuite>
-</testsuites>
+</testsuites>
\ No newline at end of file
diff --git a/packages/test-runner-junit-reporter/test/fixtures/nested/expected.xml b/packages/test-runner-junit-reporter/test/fixtures/nested/expected.xml
index d1633aa04..e8260fb00 100644
--- a/packages/test-runner-junit-reporter/test/fixtures/nested/expected.xml
+++ b/packages/test-runner-junit-reporter/test/fixtures/nested/expected.xml
@@ -1,11 +1,11 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuites>
-  <testsuite name="Chrome_puppeteer_/packages/test-runner-junit-reporter/test/fixtures/nested/nested-test.js" id="0" tests="1" skipped="0" errors="0" failures="0" time="0.001">
+  <testsuite name="Chrome_puppeteer_/packages/test-runner-junit-reporter/test/fixtures/nested/nested-test.js" id="0" tests="1" skipped="0" errors="0" failures="0" time="0.001" file="packages/test-runner-junit-reporter/test/fixtures/nested/nested-test.js">
     <properties>
       <property name="test.fileName" value="packages/test-runner-junit-reporter/test/fixtures/nested/nested-test.js"/>
       <property name="browser.name" value="Chrome"/>
       <property name="browser.launcher" value="puppeteer"/>
     </properties>
-    <testcase name="is equivalent to map (f.g) f a" time="<<computed>>" classname="given a functor f and a function a -&gt; b map f map g f a" file="packages/test-runner-junit-reporter/test/fixtures/nested/nested-test.js"/>
+    <testcase name="is equivalent to map (f.g) f a" time="<<computed>>" classname="given a functor f and a function a -&gt; b map f map g f a"/>
   </testsuite>
-</testsuites>
+</testsuites>
\ No newline at end of file
diff --git a/packages/test-runner-junit-reporter/test/fixtures/simple/expected.xml b/packages/test-runner-junit-reporter/test/fixtures/simple/expected.xml
index d2293173b..34fc363a1 100644
--- a/packages/test-runner-junit-reporter/test/fixtures/simple/expected.xml
+++ b/packages/test-runner-junit-reporter/test/fixtures/simple/expected.xml
@@ -1,25 +1,25 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuites>
-  <testsuite name="Chrome_puppeteer_/packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js" id="0" tests="6" skipped="1" errors="2" failures="2" time="0.001">
+  <testsuite name="Chrome_puppeteer_/packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js" id="0" tests="6" skipped="1" errors="2" failures="2" time="0.001" file="packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js">
     <properties>
       <property name="test.fileName" value="packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js"/>
       <property name="browser.name" value="Chrome"/>
       <property name="browser.launcher" value="puppeteer"/>
     </properties>
-    <testcase name="under addition" time="0.001" classname="real numbers forming a monoid" file="packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js"/>
-    <testcase name="null hypothesis" time="0.001" classname="off-by-one boolean logic errors" file="packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js"/>
-    <testcase name="asserts error" time="0.001" classname="off-by-one boolean logic errors" file="packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js" line="17">
+    <testcase name="under addition" time="0.001" classname="real numbers forming a monoid"/>
+    <testcase name="null hypothesis" time="0.001" classname="off-by-one boolean logic errors"/>
+    <testcase name="asserts error" time="0.001" classname="off-by-one boolean logic errors" line="17">
       <failure message="expected false to be true" type="AssertionError"><![CDATA[AssertionError: expected false to be true
   at o.<anonymous> (packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js:17:29)]]></failure>
     </testcase>
-    <testcase name="tbd: confirm true positive" time="0" classname="off-by-one boolean logic errors" file="packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js">
+    <testcase name="tbd: confirm true positive" time="0" classname="off-by-one boolean logic errors">
       <skipped/>
     </testcase>
-    <testcase name="reports logs to JUnit" time="0.001" classname="logging during a test" file="packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js"/>
-    <testcase name="fails with source trace" time="<<computed>>" classname="logging during a test" file="packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js" line="2">
+    <testcase name="reports logs to JUnit" time="0.001" classname="logging during a test"/>
+    <testcase name="fails with source trace" time="<<computed>>" classname="logging during a test" line="2">
       <failure message="failed" type="Error"><![CDATA[Error: failed
   at fail (packages/test-runner-junit-reporter/test/fixtures/simple/simple-source.js:2:9)
   at o.<anonymous> (packages/test-runner-junit-reporter/test/fixtures/simple/simple-test.js:33:17)]]></failure>
     </testcase>
   </testsuite>
-</testsuites>
+</testsuites>
\ No newline at end of file