eth/filters: avoid dangling goroutines

eth/filters/filter_system_test.go

@@ -301,12 +301,15 @@ func TestLogFilterCreation(t *testing.T) {
 	)
 
 	for i, test := range testCases {
-		_, err := api.NewFilter(test.crit)
-		if test.success && err != nil {
+		id, err := api.NewFilter(test.crit)
+		if err != nil && test.success {
 			t.Errorf("expected filter creation for case %d to success, got %v", i, err)
 		}
-		if !test.success && err == nil {
-			t.Errorf("expected testcase %d to fail with an error", i)
+		if err == nil {
+			api.UninstallFilter(id)
+			if !test.success {
+				t.Errorf("expected testcase %d to fail with an error", i)
+			}
 		}
 	}
 }