Increase unit test coverage

[googs1025]

What would you like to be added:
Try to increase the scope of unit testing, the current coverage is relatively low.
Why is this needed:
Improve unit test coverage, improve code robustness, and use this issue to track progress.

reference：#473

[googs1025]

/assign

[googs1025]

@danielvegamyhre
I tried to follow your suggestion and rewrote the demo. Please check if it meets your expectations. This is just a demo.

func TestCreateJobs(t *testing.T) {
	var (
		jobSetName = "test-jobset"
		ns         = "default"
	)
	tests := []struct {
		name                string
		js                  *jobset.JobSet
		jobs                childJobs
		expected            error
		expectedJobsCreated []*batchv1.Job
	}{
		{
			name: "create jobs",
			js: testutils.MakeJobSet(jobSetName, ns).
				ReplicatedJob(testutils.MakeReplicatedJob("replicated-job-1").
					Job(testutils.MakeJobTemplate("test-job", ns).Obj()).
					Replicas(1).
					Obj()).Obj(),
			jobs: childJobs{
				active: []*batchv1.Job{
					makeJob(&makeJobArgs{
						jobSetName:        jobSetName,
						replicatedJobName: "replicated-job-1",
						jobName:           "test-jobset-replicated-job-1-test-job-0",
						ns:                ns,
						replicas:          1,
						jobIdx:            0,
					}).Parallelism(1).
						Completions(2).
						Ready(1).
						Active(1).Obj(),
				},
			},
			expectedJobsCreated: []*batchv1.Job{
				makeJob(&makeJobArgs{
					jobSetName:        jobSetName,
					replicatedJobName: "replicated-job-1",
					jobName:           "test-jobset-replicated-job-1-test-job-0",
					ns:                ns,
					replicas:          1,
					jobIdx:            0,
				}).Parallelism(1).
					Completions(2).
					Ready(1).
					Active(1).Obj(),
			},
		},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			var jobsCreated []*batchv1.Job
			scheme := runtime.NewScheme()
			utilruntime.Must(jobset.AddToScheme(scheme))
			utilruntime.Must(corev1.AddToScheme(scheme))
			utilruntime.Must(batchv1.AddToScheme(scheme))
			fakeClient := fake.NewClientBuilder().
				WithScheme(scheme).
				WithInterceptorFuncs(interceptor.Funcs{
					Create: func(ctx context.Context, client client.WithWatch, obj client.Object, opts ...client.CreateOption) error {
						job, ok := obj.(*batchv1.Job)
						if !ok {
							return nil
						}
						job = tc.jobs.active[0]
						jobsCreated = append(jobsCreated, job)
						return nil
					},
				}).
				Build()
			r := &JobSetReconciler{
				Client: fakeClient,
				Scheme: scheme,
				Record: nil,
			}

			err := r.createJobs(context.TODO(), tc.js, &tc.jobs, tc.js.Status.ReplicatedJobsStatus)
			if err != tc.expected {
				t.Errorf("createJobs() returned unexpected error: got %v, want %v", err, tc.expected)
			}
			sort.Slice(jobsCreated, func(i, j int) bool {
				return jobsCreated[i].Name < jobsCreated[j].Name
			})
			sort.Slice(tc.expectedJobsCreated, func(i, j int) bool {
				return tc.expectedJobsCreated[i].Name < tc.expectedJobsCreated[j].Name
			})
			if !reflect.DeepEqual(jobsCreated, tc.expectedJobsCreated) {
				t.Errorf("createJobs() did not make the expected job creation calls")
			}
		})
	}
}

[danielvegamyhre]

@danielvegamyhre I tried to follow your suggestion and rewrote the demo. Please check if it meets your expectations. This is just a demo.

Thanks! Can you make a PR please so I can comment on it?

[googs1025]

@danielvegamyhre /PTAL pr