Add unit tests to cover the retrieval of default user by OS.

frontend/src/__tests__/util.test.tsx

@@ -1,4 +1,6 @@
-import {clamp} from '../util'
+import {clamp, clusterDefaultUser} from '../util'
+import {mock} from 'jest-mock-extended'
+import {ClusterDescription} from '../types/clusters'
 
 describe('Given a function to clamp a number using an option step discretization', () => {
   describe('when the input is below the minimum', () => {
@@ -32,3 +34,45 @@ describe('Given a function to clamp a number using an option step discretization
     })
   })
 })
+
+describe('Given a function to get the default cluster user', () => {
+  describe('when the OS is Amazon Linux 2', () => {
+    const cluster = {config: {Image: {Os: 'alinux2'}}}
+    it('should be ec2-user', () => {
+      const result = clusterDefaultUser(cluster)
+      expect(result).toBe('ec2-user')
+    })
+  })
+
+  describe('when the OS is Ubuntu 18.04', () => {
+    const cluster = {config: {Image: {Os: 'ubuntu1804'}}}
+    it('should be ec2-user', () => {
+      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', () => {
+      const result = clusterDefaultUser(cluster)
+      expect(result).toBe('ubuntu')
+    })
+  })
+
+  describe('when the OS is Ubuntu 22.04', () => {
+    const cluster = {config: {Image: {Os: 'ubuntu2204'}}}
+    it('should be ubuntu', () => {
+      const result = clusterDefaultUser(cluster)
+      expect(result).toBe('ubuntu')
+    })
+  })
+
+  describe('when the OS is Centos 7', () => {
+    const cluster = {config: {Image: {Os: 'centos7'}}}
+    it('should be centos', () => {
+      const result = clusterDefaultUser(cluster)
+      expect(result).toBe('centos')
+    })
+  })
+})