TDD之断言验证System.out.print输出

业务类：

public class OutDemo {
    public void print(String content) {
        System.out.print(content);
    }
}

测试类：

public class OutDemoTest {
    private StringBuilder systemOutput;
    @Before
    public void setUp() {
        systemOutput = injectSystemOutput();
    }
    @Test
    public void testOut() {
        OutDemo out = new  OutDemo();
        out.print("123");
        Assert.assertEquals(systemOutput.toString(), "123");
    }
    private StringBuilder injectSystemOutput() {
        StringBuilder stringBuilder = new StringBuilder();
        PrintStream outputPrintStream = new PrintStream(new OutputStream() {
            @Override
            public void write(int b) throws IOException {
                stringBuilder.append((char) b);
            }
        });
        System.setOut(outputPrintStream);
        return stringBuilder;
    }
}