@Override
    public String getProperty(final String key) {
        String value = super.getProperty(key);
        if (null != value) {
            return value;
        }
        for (Properties each : multiProps) {
            value = each.getProperty(key);
            if (null != value) {
                return value;
            }
        }
        return null;
    }
@Test
    void assertGetProperty() {
        assertThat(multiSourceProperties.getProperty("keyA"), is("valueA"));
        assertThat(multiSourceProperties.getProperty("keyB"), is("valueB"));
        assertNull(multiSourceProperties.getProperty("keyC"));
    }