如何使用 Junit 在 Java 中测试打印方法
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How to test a print method in Java using Junit
提问by Roy
I have written a method that is printing output to a console. How should I test it?
我编写了一个将输出打印到控制台的方法。我应该如何测试？
public class PrinterForConsole implements Printer<Item>{
public void printResult(List<Item> items) {
for (Item item: items){
System.out.println("Name: " + item.getName());
System.out.println("Number: " + item.getNumber());
}
}
}
currently, my test looks like this
目前，我的测试看起来像这样
public class TestPrinter{
@Test
public void printResultTest() throws Exception {
(am figuring out what to put here)
}
}
I have read the solution at this post(thanks @Codebender and @KDM for highlighting this) but don't quite understand it. How does the solution there test the print(List items) method? Hence, asking it afresh here.
我已经阅读了这篇文章中的解决方案（感谢 @Codebender 和 @KDM 强调这一点），但不太明白。那里的解决方案如何测试 print(List items) 方法？因此，在这里重新提问。
回答by Dakshinamurthy Karra
The best way to test it is by refactoring it to accept a PrintStreamas a parameter and you can pass another PrintStreamconstructed out of ByteArrayOutputStreamand check what is printed into the baos.
测试它的最好方法是重构它以接受 aPrintStream作为参数，您可以传递另一个PrintStream构造的ByteArrayOutputStream并检查打印到 baos 中的内容。
Otherwise, you can use System.setOutto set your standard output to another stream. You can verify what is written into it after the method returns.
否则，您可以使用System.setOut将标准输出设置为另一个流。您可以在方法返回后验证写入的内容。
A simplified version with comments is below:
带有注释的简化版本如下：
@Test
public void printTest() throws Exception {
// Create our test list of items
ArrayList<Item> items = new ArrayList<Item>();
items.add(new Item("KDM", 1810));
items.add(new Item("Roy", 2010));
// Keep current System.out with us
PrintStream oldOut = System.out;
// Create a ByteArrayOutputStream so that we can get the output
// from the call to print
ByteArrayOutputStream baos = new ByteArrayOutputStream();
// Change System.out to point out to our stream
System.setOut(new PrintStream(baos));
print(items);
// Reset the System.out
System.setOut(oldOut);
// Our baos has the content from the print statement
String output = new String(baos.toByteArray());
// Add some assertions out output
assertTrue(output.contains("Name: KDM"));
assertTrue(output.contains("Name: Roy"));
System.out.println(output);
}
Note that if the printmethod throws an exception, the System.outis not reset. It is better to use setupand teardownmethods to set and reset this.
请注意，如果该print方法抛出异常，System.out则不会重置。最好使用setup和teardown方法来设置和重置它。
回答by Anand Dwivedi
This is the Simple Test Code :-
这是简单的测试代码：-
@Test
public void out() {
System.out.print("hello");
assertEquals("helloworld", outContent.toString());
}
@Test
public void err() {
System.err.print("helloworld 1 ");
assertEquals("helloworld 1", errContent.toString());
}
For more :JUnit test for System.out.println()
回答by Jose Martinez
How about something like this.
这样的事情怎么样。
@Test
public void printTest() throws Exception {
OutputStream os = new ByteArrayOutputStream();
System.setOut(os);
objectInTest.print(items);
String actualOutput = os.toString("UTF-8");
assertEquals(expectedOutput, actualOutput);
}
回答by Codebender
Since you have put you don't get what the duplicate question says, I will try to explain a little.
既然你已经把你不明白重复的问题说的是什么，我会试着解释一下。
When you do, System.setOut(OutputStream), whatever the application writes to the console (using System.out.printX()) statements, instead get written to the outputStreamyou pass.
当您这样做时System.setOut(OutputStream)，无论应用程序写入控制台（使用System.out.printX()）语句，而是写入outputStream您传递的内容。
So, you can do something like,
所以，你可以做类似的事情，
public void printTest() throws Exception {
ByteArrayOutputStream outContent = new ByteArrayOutputStream();
System.setOut(new PrintStream(outContent));
// After this all System.out.println() statements will come to outContent stream.
// So, you can normally call,
print(items); // I will assume items is already initialized properly.
//Now you have to validate the output. Let's say items had 1 element.
// With name as FirstElement and number as 1.
String expectedOutput = "Name: FirstElement\nNumber: 1" // Notice the \n for new line.
// Do the actual assertion.
assertEquals(expectedOutput, outContent.toString());
}
回答by Roy
Eventually, what I came up with is this (after going through all the answers and links to possible duplicates above).
最终，我想出了这个（在浏览了所有答案和上面可能重复的链接之后）。
import org.junit.Test;
@Test
public void shouldPrintToConsole() throws Exception {
Item testItem = new Item("Name", "Number");
List<Item> items = Arrays.asList(testItem);
Printer print = new Printer();
printer.printOutput(items);
}
Read up on naming convention (shouldPrintToConsole()) for testing too. Wondering if this is the convention because I see many sites that follow and many that don't.
阅读命名约定 (shouldPrintToConsole()) 以进行测试。想知道这是否是惯例，因为我看到许多遵循的网站和许多没有遵循的网站。
