diff --git a/.github/workflows/kover.yml b/.github/workflows/kover.yml
new file mode 100644
index 0000000000..6f2095b8ab
--- /dev/null
+++ b/.github/workflows/kover.yml
@@ -0,0 +1,29 @@
+name: Measure coverage
+
+on:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+      - name: Set up JDK 17
+        uses: actions/setup-java@v3
+        with:
+          distribution: temurin
+          java-version: 17
+      - name: Setup Gradle
+        uses: gradle/gradle-build-action@v2
+      - name: Generate kover coverage report
+        run: ./gradlew koverXmlReport
+      - name: Add coverage report to PR
+        id: kover
+        uses: mi-kas/kover-report@v1
+        with:
+          path: ${{ github.workspace }}/build/reports/kover/xml/report.xml
+          token: ${{ secrets.GITHUB_TOKEN }}
+          title: Code Coverage
+          update-comment: true
\ No newline at end of file
diff --git a/build.gradle.kts b/build.gradle.kts
index d17e5f8356..f5b8e2d8d5 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -8,6 +8,9 @@ plugins {
 
     // See api/API_README.md for details
     id("org.jetbrains.kotlinx.binary-compatibility-validator") version "0.12.0"
+
+    // Coverage
+    id("org.jetbrains.kotlinx.kover") version "0.6.1"
 }
 
 group = "com.github.kwebio"
@@ -64,6 +67,8 @@ dependencies {
 
     testImplementation("org.junit.jupiter:junit-jupiter-api")
     testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine")
+
+    testImplementation("org.awaitility:awaitility:4.2.0")
 }
 
 tasks.dokkaHtml {
diff --git a/src/main/kotlin/kweb/Kweb.kt b/src/main/kotlin/kweb/Kweb.kt
index 191d911f98..21a532c0a8 100755
--- a/src/main/kotlin/kweb/Kweb.kt
+++ b/src/main/kotlin/kweb/Kweb.kt
@@ -291,7 +291,7 @@ class Kweb private constructor(
                                 message.callback != null -> {
                                     val (resultId, result) = message.callback
                                     val resultHandler = remoteClientState.handlers[resultId]
-                                        ?: error("No data handler for $resultId for client ${remoteClientState.id}")
+                                        ?: error("No resultHandler for $resultId, for client ${remoteClientState.id}")
                                     resultHandler(result)
                                 }
                                 message.keepalive -> {
diff --git a/src/test/kotlin/kweb/HistoryTest.kt b/src/test/kotlin/kweb/HistoryTest.kt
index 60b3fe9c86..8e47f87793 100644
--- a/src/test/kotlin/kweb/HistoryTest.kt
+++ b/src/test/kotlin/kweb/HistoryTest.kt
@@ -15,16 +15,18 @@ import org.openqa.selenium.WebDriver
 import org.openqa.selenium.WebElement
 import org.openqa.selenium.chrome.ChromeDriver
 import org.openqa.selenium.support.ThreadGuard
+import org.awaitility.Awaitility.*
+import java.time.Duration
 
 @ExtendWith(SeleniumJupiter::class)
-class HistoryTest(@Arguments("--headless")  unprotectedDriver: ChromeDriver) {
+class HistoryTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
 
-    val driver : WebDriver
+    val driver: WebDriver
 
     init {
         //ThreadGuard.protect ensures that the ChromeDriver can only be called by the thread that created it
         //This should make this test thread safe.
-         driver = ThreadGuard.protect(unprotectedDriver)
+        driver = ThreadGuard.protect(unprotectedDriver)
     }
 
     companion object {
@@ -47,27 +49,30 @@ class HistoryTest(@Arguments("--headless")  unprotectedDriver: ChromeDriver) {
     fun testBackButton() {
         historyTestApp.reloadCount.value shouldBe 0
         driver.get("http://localhost:7665/0")
-        driver.findElement(By.tagName("a")).let { aElement ->
-            historyTestApp.url.value shouldBe "/0"
-            aElement.click()
-            Thread.sleep(100)
-            historyTestApp.url.value shouldBe "/1"
-        }
-        driver.findElement(By.tagName("a")).let { aElement ->
-            aElement.click()
-            Thread.sleep(100)
-            historyTestApp.url.value shouldBe "/2"
-            historyTestApp.reloadCount.value shouldBe 1
+
+        historyTestApp.url.value shouldBe "/0"
+        driver.findElement(By.tagName("a")).click()
+
+        await().untilAsserted { historyTestApp.url.value shouldBe "/1" }
+
+        await().pollInSameThread().untilAsserted {
+            // For some reason was getting a StaleElementReferenceException intermittently, so put this
+            // inaide an await()
+            driver.findElement(By.tagName("a")).click()
         }
+
+        await().untilAsserted { historyTestApp.url.value shouldBe "/2" }
+        await().untilAsserted { historyTestApp.reloadCount.value shouldBe 1 }
+
         driver.navigate().back()
-        Thread.sleep(100)
-        historyTestApp.url.value shouldBe "/1"
-        historyTestApp.reloadCount.value shouldBe 1
+
+        await().untilAsserted { historyTestApp.url.value shouldBe "/1" }
+        await().untilAsserted { historyTestApp.reloadCount.value shouldBe 1 }
 
         driver.navigate().forward()
-        Thread.sleep(100)
-        historyTestApp.url.value shouldBe "/2"
-        historyTestApp.reloadCount.value shouldBe 1
+
+        await().untilAsserted { historyTestApp.url.value shouldBe "/2" }
+        await().untilAsserted { historyTestApp.reloadCount.value shouldBe 1 }
     }
 }
 
@@ -88,9 +93,11 @@ class HistoryTestApp {
             route {
                 path("/{num}") { p ->
                     render(p["num"]!!.toInt()) { num ->
-                        a().apply {
+                        a {
+                            element {
+                                href = "/${num + 1}"
+                            }
                             text("Next ($num)")
-                            href = "/${num + 1}"
                         }
                     }
                 }
diff --git a/src/test/kotlin/kweb/HrefTest.kt b/src/test/kotlin/kweb/HrefTest.kt
index 92145e570c..3b83f5951a 100644
--- a/src/test/kotlin/kweb/HrefTest.kt
+++ b/src/test/kotlin/kweb/HrefTest.kt
@@ -5,6 +5,7 @@ import io.github.bonigarcia.seljup.SeleniumJupiter
 import io.kotest.matchers.shouldBe
 import kweb.*
 import kweb.state.KVar
+import org.awaitility.Awaitility
 import org.junit.jupiter.api.AfterAll
 import org.junit.jupiter.api.BeforeAll
 import org.junit.jupiter.api.Test
@@ -49,10 +50,9 @@ class HrefTest(@Arguments("--headless") private var unprotectedDriver: ChromeDri
         hrefTestApp.appUrl.value shouldBe "/"
         hrefTestApp.renderCount.value shouldBe 1
         aElement.click()
-        Thread.sleep(100)
-        hrefTestApp.appUrl.value shouldBe "/two"
+        Awaitility.await().untilAsserted { hrefTestApp.appUrl.value shouldBe "/two" }
         // Page shouldn't have been re-rendered for a relative link
-        hrefTestApp.renderCount.value shouldBe 1
+        Awaitility.await().untilAsserted { hrefTestApp.renderCount.value shouldBe 1 }
     }
 
 
diff --git a/src/test/kotlin/kweb/InputCheckedTest.kt b/src/test/kotlin/kweb/InputCheckedTest.kt
index 857499d806..755bfbd829 100644
--- a/src/test/kotlin/kweb/InputCheckedTest.kt
+++ b/src/test/kotlin/kweb/InputCheckedTest.kt
@@ -5,6 +5,8 @@ import io.github.bonigarcia.seljup.SeleniumJupiter
 import io.kotest.matchers.shouldBe
 import kweb.*
 import kweb.state.KVar
+import org.awaitility.Awaitility
+import org.awaitility.Awaitility.await
 import org.junit.jupiter.api.AfterAll
 import org.junit.jupiter.api.BeforeAll
 import org.junit.jupiter.api.Test
@@ -44,17 +46,13 @@ class InputCheckedTest(@Arguments("--headless") unprotectedDriver: ChromeDriver)
         val input = driver.findElement(By.tagName("input"))
         inputCheckedTestApp.checkKVar.value shouldBe false
         input.click()
-        Thread.sleep(100)
-        inputCheckedTestApp.checkKVar.value shouldBe true
-        Thread.sleep(100)
+        await().untilAsserted { inputCheckedTestApp.checkKVar.value shouldBe true }
         input.click()
-        Thread.sleep(100)
-        inputCheckedTestApp.checkKVar.value shouldBe false
+        await().untilAsserted { inputCheckedTestApp.checkKVar.value shouldBe false }
 
-        input.getAttribute("checked") shouldBe null
+        await().untilAsserted { input.getAttribute("checked") shouldBe null }
         inputCheckedTestApp.checkKVar.value = true
-        Thread.sleep(100)
-        input.getAttribute("checked") shouldBe "true"
+        await().untilAsserted { input.getAttribute("checked") shouldBe "true" }
     }
 }
 
diff --git a/src/test/kotlin/kweb/SelectValueTest.kt b/src/test/kotlin/kweb/SelectValueTest.kt
index 72fad4c12b..322ae29e2a 100644
--- a/src/test/kotlin/kweb/SelectValueTest.kt
+++ b/src/test/kotlin/kweb/SelectValueTest.kt
@@ -5,6 +5,7 @@ import io.github.bonigarcia.seljup.SeleniumJupiter
 import io.kotest.matchers.shouldBe
 import kweb.*
 import kweb.state.KVar
+import org.awaitility.Awaitility
 import org.junit.jupiter.api.AfterAll
 import org.junit.jupiter.api.BeforeAll
 import org.junit.jupiter.api.Test
@@ -43,14 +44,11 @@ class SelectValueTest(@Arguments("--headless") unprotectedDriver: ChromeDriver)
     fun mainTest() {
         driver.get("http://localhost:7668/")
         val select = Select(driver.findElement(By.tagName("select")))
-        selectValueTestApp.selectValue.value shouldBe ""
-        Thread.sleep(100)
+        Awaitility.await().untilAsserted { selectValueTestApp.selectValue.value shouldBe "" }
         select.selectByValue("cat")
-        Thread.sleep(100)
-        selectValueTestApp.selectValue.value shouldBe "cat"
+        Awaitility.await().untilAsserted { selectValueTestApp.selectValue.value shouldBe "cat" }
         select.selectByValue("dog")
-        Thread.sleep(100)
-        selectValueTestApp.selectValue.value shouldBe "dog"
+        Awaitility.await().untilAsserted { selectValueTestApp.selectValue.value shouldBe "dog" }
     }
 }
 
diff --git a/src/test/kotlin/kweb/state/render/RenderEachTest.kt b/src/test/kotlin/kweb/state/render/RenderEachTest.kt
index 81f0e9ecb7..7ff56e328d 100644
--- a/src/test/kotlin/kweb/state/render/RenderEachTest.kt
+++ b/src/test/kotlin/kweb/state/render/RenderEachTest.kt
@@ -6,6 +6,8 @@ import io.kotest.matchers.shouldBe
 import kweb.*
 import kweb.state.ObservableList
 import kweb.state.renderEach
+import org.awaitility.Awaitility
+import org.awaitility.Awaitility.await
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.extension.ExtendWith
 import org.openqa.selenium.By
@@ -49,13 +51,14 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElements(By.tagName("button"))
         button[0].click()
-        Thread.sleep(50)
-        val labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe "Moose"
-        labels[1].text shouldBe "Dog"
-        labels[2].text shouldBe "Cat"
-        labels[3].text shouldBe "Bear"
-        labels[4].text shouldBe "Horse"
+        await().pollInSameThread().untilAsserted {
+            val labels = driver.findElements(By.tagName("h1"))
+            labels[0].text shouldBe "Moose"
+            labels[1].text shouldBe "Dog"
+            labels[2].text shouldBe "Cat"
+            labels[3].text shouldBe "Bear"
+            labels[4].text shouldBe "Horse"
+        }
         server.close()
     }
 
@@ -81,13 +84,14 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElements(By.tagName("button"))
         button[0].click()
-        Thread.sleep(50)
         val labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe ("Dog")
-        labels[1].text shouldBe ("Cat")
-        labels[2].text shouldBe ("Bear")
-        labels[3].text shouldBe ("Horse")
-        labels[4].text shouldBe ("Moose")
+        await().untilAsserted {
+            labels[0].text shouldBe ("Dog")
+            labels[1].text shouldBe ("Cat")
+            labels[2].text shouldBe ("Bear")
+            labels[3].text shouldBe ("Horse")
+            labels[4].text shouldBe ("Moose")
+        }
         server.close()
     }
 
@@ -113,13 +117,14 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElements(By.tagName("button"))
         button[0].click()
-        Thread.sleep(50)
-        val labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe "Dog"
-        labels[1].text shouldBe "Cat"
-        labels[2].text shouldBe "Moose"
-        labels[3].text shouldBe "Bear"
-        labels[4].text shouldBe "Horse"
+        await().pollInSameThread().untilAsserted {
+            val labels = driver.findElements(By.tagName("h1"))
+            labels[0].text shouldBe "Dog"
+            labels[1].text shouldBe "Cat"
+            labels[2].text shouldBe "Moose"
+            labels[3].text shouldBe "Bear"
+            labels[4].text shouldBe "Horse"
+        }
         server.close()
     }
 
@@ -145,9 +150,10 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElements(By.tagName("button"))
         button[0].click()
-        Thread.sleep(50)
         val labels = driver.findElements(By.tagName("h1"))
-        labels[1].text shouldBe "Horse"
+        await().untilAsserted {
+            labels[1].text shouldBe "Horse"
+        }
         server.close()
     }
 
@@ -183,25 +189,29 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElements(By.tagName("button"))
         button[0].click()
-        Thread.sleep(50)
-        var labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe "Aardvark"
-        labels[1].text shouldBe "Cow"
-        labels[2].text shouldBe "Dog"
-        labels[3].text shouldBe "Elephant"
+
+        await().pollInSameThread().untilAsserted {
+            var labels = driver.findElements(By.tagName("h1"))
+            labels[0].text shouldBe "Aardvark"
+            labels[1].text shouldBe "Cow"
+            labels[2].text shouldBe "Dog"
+            labels[3].text shouldBe "Elephant"
+        }
 
         button[1].click()
-        Thread.sleep(50)
-        labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe "Cow"
-        labels[1].text shouldBe "Dog"
-        labels[2].text shouldBe "Elephant"
+        await().pollInSameThread().untilAsserted {
+            val labels = driver.findElements(By.tagName("h1"))
+            labels[0].text shouldBe "Cow"
+            labels[1].text shouldBe "Dog"
+            labels[2].text shouldBe "Elephant"
+        }
 
         button[2].click()
-        Thread.sleep(50)
-        labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe "Cow"
-        labels[1].text shouldBe "Dog"
+        await().pollInSameThread().untilAsserted {
+            val labels = driver.findElements(By.tagName("h1"))
+            labels[0].text shouldBe "Cow"
+            labels[1].text shouldBe "Dog"
+        }
         server.close()
     }
 
@@ -227,13 +237,14 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElement(By.tagName("button"))
         button.click()
-        Thread.sleep(50)
-        val labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe "Dog"
-        labels[1].text shouldBe "Cat"
-        labels[2].text shouldBe "Horse"
-        labels[3].text shouldBe "Bear"
-        labels[4].text shouldBe "Moose"
+        await().pollInSameThread().untilAsserted {
+            val labels = driver.findElements(By.tagName("h1"))
+            labels[0].text shouldBe "Dog"
+            labels[1].text shouldBe "Cat"
+            labels[2].text shouldBe "Horse"
+            labels[3].text shouldBe "Bear"
+            labels[4].text shouldBe "Moose"
+        }
         server.close()
     }
 
@@ -259,13 +270,14 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElement(By.tagName("button"))
         button.click()
-        Thread.sleep(50)
-        val labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe "Cat"
-        labels[1].text shouldBe "Bear"
-        labels[2].text shouldBe "Moose"
-        labels[3].text shouldBe "Horse"
-        labels[4].text shouldBe "Dog"
+       await().pollInSameThread().untilAsserted {
+           val labels = driver.findElements(By.tagName("h1"))
+           labels[0].text shouldBe "Cat"
+           labels[1].text shouldBe "Bear"
+           labels[2].text shouldBe "Moose"
+           labels[3].text shouldBe "Horse"
+           labels[4].text shouldBe "Dog"
+       }
         server.close()
     }
 
@@ -291,13 +303,14 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElement(By.tagName("button"))
         button.click()
-        Thread.sleep(50)
-        val labels = driver.findElements(By.tagName("h1"))
-        labels[0].text shouldBe "Horse"
-        labels[1].text shouldBe "Dog"
-        labels[2].text shouldBe "Cat"
-        labels[3].text shouldBe "Bear"
-        labels[4].text shouldBe "Moose"
+        await().pollInSameThread().untilAsserted {
+            val labels = driver.findElements(By.tagName("h1"))
+            labels[0].text shouldBe "Horse"
+            labels[1].text shouldBe "Dog"
+            labels[2].text shouldBe "Cat"
+            labels[3].text shouldBe "Bear"
+            labels[4].text shouldBe "Moose"
+        }
         server.close()
     }
 
@@ -323,9 +336,10 @@ class RenderEachTest(@Arguments("--headless") unprotectedDriver: ChromeDriver) {
         driver.get("http://localhost:1234")
         val button = driver.findElement(By.tagName("button"))
         button.click()
-        Thread.sleep(50)
-        val labels = driver.findElements(By.tagName("h1"))
-        labels.size shouldBe 0
+        await().pollInSameThread().untilAsserted {
+            val labels = driver.findElements(By.tagName("h1"))
+            labels.size shouldBe 0
+        }
         server.close()
     }