设置属性“ java.io.tmpdir”会导致测试失败

Question

I created a class to generate temporary files. After that I started to test the class and wrote 2 tests, see below. I excluded my generator class to be sure that none of my code causes interference.

public class TemporaryFileGeneratorTest {

    private static final String SYSTEM_TEMP_DIR_PROP = "java.io.tmpdir";

    private static final String DEFAULT_TEMP_DIR = System.getProperty(SYSTEM_TEMP_DIR_PROP);

    @Before
    public void setDefaultTempDir() {
        System.setProperty(SYSTEM_TEMP_DIR_PROP, DEFAULT_TEMP_DIR);
    }

    @Test
    public void testCreateTemporaryFile() throws IOException {
        File file = File.createTempFile("temp-file", ".txt");
        file.deleteOnExit();
    }

    @Test(expected = IOException.class)
    public void testCreateTemporaryFileShouldThrowException() throws IOException {
        System.setProperty(SYSTEM_TEMP_DIR_PROP, "not-existing");
        File file = File.createTempFile("cannot-create-file", ".txt");
    }
}

If I run the tests one-by-one, both of the tests will run successfully. But in the case of running the whole test file (by eclipse) the 'testCreateTemporaryFileShouldThrowException' will run in the first place - successfully, and 'testCreateTemporaryFile' will run secondly - with a failure. The failure is caused by an IOException:

java.io.IOException: The system cannot find the path specified
    at java.io.WinNTFileSystem.createFileExclusively(Native Method)
    at java.io.File.createTempFile(File.java:2024)
    at java.io.File.createTempFile(File.java:2070)
    at mypackage.TemporaryFileGeneratorTest.testCreateTemporaryFile(TemporaryFileGeneratorTest.java:14)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:89)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)

Anyone got an idea what is wrong? I set the system property "java.io.tmpdir" always before a test runs and this is the only change that the second test makes that needs to be reset.

Answer 1

Doing this way will work:

        @Test
        public void testCreateTemporaryFile() throws IOException {
            File file = File.createTempFile("temp-file", ".txt", new File(System.getProperty(SYSTEM_TEMP_DIR_PROP)));
            file.deleteOnExit();
        }

        @Test(expected = IOException.class)
        public void testCreateTemporaryFileShouldThrowException() throws IOException {
            System.setProperty(SYSTEM_TEMP_DIR_PROP, "not-existing");
            File file = File.createTempFile("cannot-create-file", ".txt", new File(System.getProperty(SYSTEM_TEMP_DIR_PROP)));
        }

It seems that you need to define the directory where Java will create your temp file. So, you need to set the third parameter of the method createTempFile which is the directory.

Not setting this parameter, Java gets lost, not finding the correct path. It might happen because you are changing an important system property.