diff --git a/__tests__/mandrel.test.ts b/__tests__/mandrel.test.ts
new file mode 100644
index 0000000..368eae9
--- /dev/null
+++ b/__tests__/mandrel.test.ts
@@ -0,0 +1,56 @@
+import * as path from 'path'
+import * as mandrel from '../src/mandrel'
+import {expect, test} from '@jest/globals'
+import {getLatestRelease} from '../src/utils'
+
+process.env['RUNNER_TOOL_CACHE'] = path.join(__dirname, 'TOOL_CACHE')
+process.env['RUNNER_TEMP'] = path.join(__dirname, 'TEMP')
+
+test('request invalid version/javaVersion combination', async () => {
+  for (var combination of [
+    ['mandrel-23.1.1.0-Final', '17'],
+    ['mandrel-23.0.2.1-Final', '21'],
+  ]) {
+    let error = new Error('unexpected')
+    try {
+      await mandrel.setUpMandrel(combination[0], combination[1])
+    } catch (err) {
+      if (!(err instanceof Error)) {
+        fail(`Unexpected non-Error: ${err}`)
+      }
+      error = err
+    }
+
+    expect(error).not.toBeUndefined()
+    expect(error.message).toContain('Failed to download')
+    expect(error.message).toContain('Are you sure version')
+  }
+})
+test('request invalid version', async () => {
+  for (var combination of [
+    ['mandrel-23.1.1.0', '21'],
+    ['mandrel-23.0.2.1', '17'],
+  ]) {
+    let error = new Error('unexpected')
+    try {
+      await mandrel.setUpMandrel(combination[0], combination[1])
+    } catch (err) {
+      if (!(err instanceof Error)) {
+        fail(`Unexpected non-Error: ${err}`)
+      }
+      error = err
+    }
+
+    expect(error).not.toBeUndefined()
+    expect(error.message).toContain('Failed to download')
+    expect(error.message).toContain('Are you sure version')
+  }
+})
+
+test('find latest', async () => {
+  // Make sure the action can find the latest Mandrel release
+  const latestRelease = await getLatestRelease(mandrel.MANDREL_REPO)
+  const tag_name = latestRelease.tag_name
+  expect(tag_name).toContain(mandrel.MANDREL_TAG_PREFIX)
+})
+
diff --git a/src/mandrel.ts b/src/mandrel.ts
index 7c015f8..ebd39fc 100644
--- a/src/mandrel.ts
+++ b/src/mandrel.ts
@@ -1,9 +1,10 @@
 import * as c from './constants'
 import {downloadExtractAndCacheJDK, getLatestRelease} from './utils'
 import {downloadTool} from '@actions/tool-cache'
+import {basename} from 'path'
 
-const MANDREL_REPO = 'mandrel'
-const MANDREL_TAG_PREFIX = c.MANDREL_NAMESPACE
+export const MANDREL_REPO = 'mandrel'
+export const MANDREL_TAG_PREFIX = c.MANDREL_NAMESPACE
 const MANDREL_DL_BASE = 'https://github.com/graalvm/mandrel/releases/download'
 
 export async function setUpMandrel(
@@ -45,16 +46,37 @@ async function setUpMandrelRelease(
   version: string,
   javaVersion: string
 ): Promise<string> {
-  const identifier = determineMandrelIdentifier(version, javaVersion)
-  const downloadUrl = `${MANDREL_DL_BASE}/${MANDREL_TAG_PREFIX}${version}/${identifier}${c.GRAALVM_FILE_EXTENSION}`
   const toolName = determineToolName(javaVersion)
   return downloadExtractAndCacheJDK(
-    async () => downloadTool(downloadUrl),
+    async () => downloadMandrelJDK(version, javaVersion),
     toolName,
     version
   )
 }
 
+async function downloadMandrelJDK(
+  version: string,
+  javaVersion: string
+): Promise<string> {
+  const identifier = determineMandrelIdentifier(version, javaVersion)
+  const downloadUrl = `${MANDREL_DL_BASE}/${MANDREL_TAG_PREFIX}${version}/${identifier}${c.GRAALVM_FILE_EXTENSION}`
+  try {
+    return await downloadTool(downloadUrl)
+  } catch (error) {
+    if (error instanceof Error && error.message.includes('404')) {
+      // Not Found
+      throw new Error(
+        `Failed to download ${basename(
+          downloadUrl
+        )}. Are you sure version: '${version}' and java-version: '${javaVersion}' are correct?`
+      )
+    }
+    throw new Error(
+      `Failed to download ${basename(downloadUrl)} (error: ${error}).`
+    )
+  }
+}
+
 function determineMandrelIdentifier(
   version: string,
   javaVersion: string