diff --git a/compiler/test/dotty/tools/dotc/profile/ChromeTraceTest.scala b/compiler/test/dotty/tools/dotc/profile/ChromeTraceTest.scala
new file mode 100644
index 000000000000..143c6b37dad5
--- /dev/null
+++ b/compiler/test/dotty/tools/dotc/profile/ChromeTraceTest.scala
@@ -0,0 +1,90 @@
+package dotty.tools.dotc.profile
+
+import java.io.*
+
+import org.junit.Assert.*
+import org.junit.*
+import java.nio.file.Files
+import java.nio.charset.StandardCharsets
+import java.util.concurrent.locks.LockSupport
+import scala.concurrent.duration.*
+
+class ChromeTraceTest:
+  private def testTraceOutputs(generator: ChromeTrace => Unit)(checkContent: String => Unit): Unit = {
+    val outfile = Files.createTempFile("trace-", ".json").nn
+    val tracer = new ChromeTrace(outfile)
+    try generator(tracer)
+    finally tracer.close()
+    val content = scala.io.Source.fromFile(outfile.toFile().nn).mkString
+    checkContent(content)
+  }
+
+  @Test def traceCounterEvent(): Unit = testTraceOutputs{ tracer =>
+    tracer.traceCounterEvent("foo", "counter1", 42, processWide = true)
+    tracer.traceCounterEvent("bar", "counter2", 21, processWide = false)
+  }{
+    case s"""{"traceEvents":[
+{"cat":"scalac","name":"foo","ph":"C","tid":"${tid1}","pid":"${pid1}","ts":${ts1},"args":{"counter1":42}}
+,{"cat":"scalac","name":"bar","ph":"C","tid":"${tid2}","pid":"${pid2}","ts":${ts2},"args":{"counter2":21}}
+]}""" =>
+    assertEquals(tid1, tid2)
+    assertTrue(tid1.toIntOption.isDefined)
+    assertNotEquals(pid1, pid2)
+    assertTrue(pid1.toIntOption.isDefined)
+    assertEquals(s"$pid1-$tid1", pid2)
+    assertTrue(ts1.toLong < ts2.toLong)
+  }
+
+  @Test def traceDurationEvent(): Unit = testTraceOutputs{ tracer =>
+    tracer.traceDurationEvent(name = "name1", startNanos = 1000L, durationNanos = 2500L,  tid = "this-thread")
+    tracer.traceDurationEvent(name = "name2", startNanos = 1000L, durationNanos = 5000L,  tid = "this-thread", pidSuffix = "pidSuffix")
+  }{
+    case s"""{"traceEvents":[
+{"cat":"scalac","name":"name1","ph":"X","tid":"this-thread","pid":"${pid1}","ts":1,"dur":2}
+,{"cat":"scalac","name":"name2","ph":"X","tid":"this-thread","pid":"${pid2}","ts":1,"dur":5}
+]}""" =>
+    assertTrue(pid1.toIntOption.isDefined)
+    assertEquals(s"$pid1-pidSuffix", pid2)
+  }
+
+  @Test def traceDurationEvents(): Unit = {
+    val testStart = System.nanoTime()
+    testTraceOutputs{ tracer =>
+    tracer.traceDurationEventStart(cat = "test1", name = "event1")
+    LockSupport.parkNanos(2.millis.toNanos)
+    tracer.traceDurationEventStart(cat = "test2", name = "event2", colour = "RED", pidSuffix = "pid-suffix")
+    LockSupport.parkNanos(4.millis.toNanos)
+    tracer.traceDurationEventEnd(cat = "test2", name = "event2")
+    LockSupport.parkNanos(8.millis.toNanos)
+    tracer.traceDurationEventEnd(cat = "test1", name = "event1", colour = "RED", pidSuffix = "pid-suffix")
+  }{
+    case s"""{"traceEvents":[
+{"cat":"test1","name":"event1","ph":"B","pid":"${pid1}","tid":"${tid1}","ts":${ts1}}
+,{"cat":"test2","name":"event2","ph":"B","pid":"${pid2}","tid":"${tid2}","ts":${ts2},"cname":"RED"}
+,{"cat":"test2","name":"event2","ph":"E","pid":"${pid3}","tid":"${tid3}","ts":${ts3}}
+,{"cat":"test1","name":"event1","ph":"E","pid":"${pid4}","tid":"${tid4}","ts":${ts4},"cname":"RED"}
+]}""" =>
+    val traceEnd = System.nanoTime()
+    assertTrue(tid1.toIntOption.isDefined)
+    assertEquals(pid1, pid3)
+    assertTrue(pid1.endsWith(s"-$tid1"))
+    assertEquals(pid2, pid4)
+    assertTrue(pid2.endsWith("-pid-suffix"))
+    List(tid1, tid2, tid3).foreach: tid =>
+      assertEquals(tid4, tid)
+    List(pid1, pid2, pid3, pid4).foreach: pid =>
+      assertTrue(pid.takeWhile(_ != '-').toIntOption.isDefined)
+
+    List(ts1, ts2, ts3, ts4).map(_.toLong) match {
+      case all @ List(ts1, ts2, ts3, ts4) =>
+        all.foreach: ts =>
+          // Timestamps are presented using Epoch microsecondos
+          assertTrue(ts >= testStart / 1000)
+          assertTrue(ts <= traceEnd / 1000)
+        assertTrue(ts2 >= ts1 + 2.millis.toMicros)
+        assertTrue(ts3 >= ts2 + 4.millis.toMicros)
+        assertTrue(ts4 >= ts3 + 8.millis.toMicros)
+      case _ => fail("unreachable")
+    }
+  }
+}
diff --git a/compiler/test/dotty/tools/dotc/profile/FileUtilsTest.scala b/compiler/test/dotty/tools/dotc/profile/FileUtilsTest.scala
new file mode 100644
index 000000000000..3253cff52057
--- /dev/null
+++ b/compiler/test/dotty/tools/dotc/profile/FileUtilsTest.scala
@@ -0,0 +1,91 @@
+package dotty.tools.dotc.profile
+
+import java.io.*
+
+import org.junit.Assert.*
+import org.junit.*
+
+class FileUtilsTest {
+
+  @Test def writeIsSame(): Unit = {
+    val fileTest = File.createTempFile("FileUtilsTest", "t1").nn
+    val fileExpected = File.createTempFile("FileUtilsTest", "t2").nn
+
+    val sTest = FileUtils.newAsyncBufferedWriter(new FileWriter(fileTest), threadsafe = false)
+    val sExpected = new BufferedWriter(new FileWriter(fileExpected))
+
+    def writeBoth(s:String, asChars: Boolean) = {
+      if (asChars) {
+        sTest.write(s.toCharArray)
+        sExpected.write(s.toCharArray)
+      } else {
+        sTest.write(s)
+        sExpected.write(s)
+      }
+    }
+
+    for (i <- 1 to 2000) {
+      writeBoth(s"line $i text;", asChars = true)
+      writeBoth(s"line $i chars", asChars = false)
+      sTest.newLine()
+      sExpected.newLine()
+    }
+    sTest.close()
+    sExpected.close()
+
+    assertEquals(fileExpected.length(),fileTest.length())
+
+    val expIn = new BufferedReader(new FileReader(fileExpected))
+    val testIn = new BufferedReader(new FileReader(fileTest))
+
+    var exp = expIn.readLine()
+    while (exp ne null) {
+      val actual = testIn.readLine()
+      assertEquals(exp, actual)
+      exp = expIn.readLine()
+    }
+    expIn.close()
+    testIn.close()
+    fileTest.delete()
+    fileExpected.delete()
+  }
+
+  @Ignore
+  @Test def showPerformance(): Unit = {
+    //warmup
+    for (i <- 1 to 1000) {
+      writeIsSame()
+    }
+
+    val fileTest = File.createTempFile("FileUtilsTest", "t1").nn
+    val fileExpected = File.createTempFile("FileUtilsTest", "t2").nn
+
+    for (i <- 1 to 10) {
+      val sTest = FileUtils.newAsyncBufferedWriter(fileTest.toPath.nn)
+      val sExpected = new BufferedWriter(new FileWriter(fileExpected))
+
+      val t1 = System.nanoTime()
+      List.tabulate(10000) {i =>
+        sTest.write(s"line $i text;")
+        sTest.newLine()
+      }
+      val t2 = System.nanoTime()
+      sTest.close()
+      val t3 = System.nanoTime()
+      List.tabulate(10000) {i =>
+        sExpected.write(s"line $i text;")
+        sExpected.newLine()
+      }
+      val t4 = System.nanoTime()
+      sExpected.close()
+
+      println(s"async    took ${t2 - t1} ns")
+      println(s"buffered took ${t4 - t3} ns")
+
+      fileTest.delete()
+      fileExpected.delete()
+    }
+  }
+
+}
+