### Question:
ExpressionLanguage { public static String channelFromFormula(String formula) { FormulaAst ast = FormulaAst.singleChannel(formula); if (ast == null) { return null; } else { return (String) ast.getValue(); } } private  ExpressionLanguage(); static String channelFromFormula(String formula); static DesiredRateReadWriteExpression<?, Object> formula(String formula); static DesiredRateReadWriteExpression<?, Object> formula(FormulaAst ast); static DesiredRateExpression<?> formulaArg(String formula); static DesiredRateExpression<T> formula(String formula, Class<T> readType);  }### Answer:
@Test public void channelFromFormula1() { assertThat(ExpressionLanguage.channelFromFormula("='test'"), equalTo("test")); }
@Test public void channelFromFormula2() { assertThat(ExpressionLanguage.channelFromFormula("=test()"), nullValue()); }
@Test public void channelFromFormula3() { assertThat(ExpressionLanguage.channelFromFormula("='test'"), equalTo("test")); }
@Test public void channelFromFormula4() { assertThat(ExpressionLanguage.channelFromFormula("='2+3'"), equalTo("2+3")); }
@Test public void channelFromFormula5() { assertThat(ExpressionLanguage.channelFromFormula("=2+3"), nullValue()); }
@Test public void channelFromFormula6() { assertThat(ExpressionLanguage.channelFromFormula("2+3"), equalTo("2+3")); }