add a test case for HostnameOverride

modify

cmd/kube-proxy/app/server_test.go

@@ -381,16 +381,24 @@ func TestProcessHostnameOverrideFlag(t *testing.T) {
 		name                 string
 		hostnameOverrideFlag string
 		expectedHostname     string
+		expectError          bool
 	}{
 		{
 			name:                 "Hostname from config file",
 			hostnameOverrideFlag: "",
 			expectedHostname:     "foo",
+			expectError:          false,
 		},
 		{
 			name:                 "Hostname from flag",
 			hostnameOverrideFlag: "  bar ",
 			expectedHostname:     "bar",
+			expectError:          false,
+		},
+		{
+			name:                 "Hostname is space",
+			hostnameOverrideFlag: "   ",
+			expectError:          true,
 		},
 	}
 	for _, tc := range testCases {
@@ -403,9 +411,15 @@ func TestProcessHostnameOverrideFlag(t *testing.T) {
 			options.hostnameOverride = tc.hostnameOverrideFlag
 
 			err := options.processHostnameOverrideFlag()
-			assert.NoError(t, err, "unexpected error %v", err)
+			if tc.expectError {
-			if tc.expectedHostname != options.config.HostnameOverride {
+				if err == nil {
-				t.Fatalf("expected hostname: %s, but got: %s", tc.expectedHostname, options.config.HostnameOverride)
+					t.Fatalf("should error for this case %s", tc.name)
+				}
+			} else {
+				assert.NoError(t, err, "unexpected error %v", err)
+				if tc.expectedHostname != options.config.HostnameOverride {
+					t.Fatalf("expected hostname: %s, but got: %s", tc.expectedHostname, options.config.HostnameOverride)
+				}
 			}
 		})
 	}