Add deafault user tests for rhel8 and rhel9

Signed-off-by: Judy Ng <njud@amazon.com>

Author: judysng

frontend/src/__tests__/util.test.tsx

@@ -44,6 +44,14 @@ describe('Given a function to get the default cluster user', () => {
     })
   })
 
+  describe('when the OS is Ubuntu 18.04', () => {
+    const cluster = {config: {Image: {Os: 'ubuntu1804'}}}
+    it('should be ubuntu', () => {
+      const result = clusterDefaultUser(cluster)
+      expect(result).toBe('ubuntu')
+    })
+  })
+
   describe('when the OS is Ubuntu 20.04', () => {
     const cluster = {config: {Image: {Os: 'ubuntu2004'}}}
     it('should be ubuntu', () => {
@@ -67,4 +75,20 @@ describe('Given a function to get the default cluster user', () => {
       expect(result).toBe('centos')
     })
   })
+
+  describe('when the OS is Rhel 8', () => {
+    const cluster = {config: {Image: {Os: 'rhel8'}}}
+    it('should be ec2-user', () => {
+      const result = clusterDefaultUser(cluster)
+      expect(result).toBe('ec2-user')
+    })
+  })
+
+  describe('when the OS is Rhel 9', () => {
+    const cluster = {config: {Image: {Os: 'rhel9'}}}
+    it('should be ec2-user', () => {
+      const result = clusterDefaultUser(cluster)
+      expect(result).toBe('ec2-user')
+    })
+  })
 })