diff --git a/lsp-sample/client/src/test/completion.test.ts b/lsp-sample/client/src/test/completion.test.ts
index fc6b81d5..2458f728 100644
--- a/lsp-sample/client/src/test/completion.test.ts
+++ b/lsp-sample/client/src/test/completion.test.ts
@@ -1,15 +1,15 @@
-import * as vscode from 'vscode';
-import { testCompletion, getDocUri } from './helper';
+import * as vscode from 'vscode'
+import { testCompletion, getDocUri } from './helper'
 
 describe('Should do completion', () => {
   const docUri = getDocUri('completion.txt')
 
-  it('Completes JS/TS', async () => {
+  it('Completes JS/TS in txt file', async () => {
     await testCompletion(docUri, new vscode.Position(0, 0), {
       items: [
         { label: 'JavaScript', kind: vscode.CompletionItemKind.Text },
         { label: 'TypeScript', kind: vscode.CompletionItemKind.Text }
       ]
-    });
+    })
   })
 })
diff --git a/lsp-sample/client/src/test/diagnostics.test.ts b/lsp-sample/client/src/test/diagnostics.test.ts
new file mode 100644
index 00000000..cdb099cd
--- /dev/null
+++ b/lsp-sample/client/src/test/diagnostics.test.ts
@@ -0,0 +1,20 @@
+import * as vscode from 'vscode'
+import { testDiagnostics, getDocUri } from './helper'
+
+describe('Should get diagnostics', () => {
+  const docUri = getDocUri('diagnostics.txt')
+
+  it('Diagnoses uppercase texts', async () => {
+    await testDiagnostics(docUri, [
+      { message: 'ANY is all uppercase.', range: toRange(0, 0, 0, 3), severity: vscode.DiagnosticSeverity.Warning, source: 'ex' },
+      { message: 'ANY is all uppercase.', range: toRange(0, 14, 0, 17), severity: vscode.DiagnosticSeverity.Warning, source: 'ex' },
+      { message: 'OS is all uppercase.', range: toRange(0, 18, 0, 20), severity: vscode.DiagnosticSeverity.Warning, source: 'ex' }
+    ])
+  })
+})
+
+function toRange(sLine: number, sChar: number, eLine: number, eChar: number) {
+  const start = new vscode.Position(sLine, sChar)
+  const end = new vscode.Position(eLine, eChar)
+  return new vscode.Range(start, end)
+}
\ No newline at end of file
diff --git a/lsp-sample/client/src/test/helper.ts b/lsp-sample/client/src/test/helper.ts
index a5d69bbc..16cc63d2 100644
--- a/lsp-sample/client/src/test/helper.ts
+++ b/lsp-sample/client/src/test/helper.ts
@@ -38,16 +38,31 @@ export async function setTestContent(content: string): Promise<boolean> {
 export async function testCompletion(docUri: vscode.Uri, position: vscode.Position, expectedCompletionList: vscode.CompletionList) {
   await activate(docUri)
 
-  const result = (await vscode.commands.executeCommand(
+  const actualCompletionList = (await vscode.commands.executeCommand(
     'vscode.executeCompletionItemProvider',
     docUri,
     position
   )) as vscode.CompletionList
 
-  assert.equal(result.items.length, expectedCompletionList.items.length);
+  assert.equal(actualCompletionList.items.length, expectedCompletionList.items.length);
   expectedCompletionList.items.forEach((expectedItem, i) => {
-    const resulItem = result.items[i]
-    assert.equal(resulItem.label, expectedItem.label)
-    assert.equal(resulItem.kind, expectedItem.kind)
+    const actualItem = actualCompletionList.items[i]
+    assert.equal(actualItem.label, expectedItem.label)
+    assert.equal(actualItem.kind, expectedItem.kind)
+  })
+} 
+
+export async function testDiagnostics(docUri: vscode.Uri, expectedDiagnostics: vscode.Diagnostic[]) {
+  await activate(docUri)
+
+  const actualDiagnostics = vscode.languages.getDiagnostics(docUri);
+
+  assert.equal(actualDiagnostics.length, expectedDiagnostics.length);
+
+  expectedDiagnostics.forEach((expectedDiagnostic, i) => {
+    const actualDiagnostic = actualDiagnostics[i]
+    assert.equal(actualDiagnostic.message, expectedDiagnostic.message)
+    assert.deepEqual(actualDiagnostic.range, expectedDiagnostic.range)
+    assert.equal(actualDiagnostic.severity, expectedDiagnostic.severity)
   })
 } 
\ No newline at end of file
diff --git a/lsp-sample/client/testFixture/diagnostics.txt b/lsp-sample/client/testFixture/diagnostics.txt
new file mode 100644
index 00000000..d910cfb5
--- /dev/null
+++ b/lsp-sample/client/testFixture/diagnostics.txt
@@ -0,0 +1 @@
+ANY browsers, ANY OS.
\ No newline at end of file