CODEWITHSUNDEEP
javajunit4mockito
user2654241
user2654241

Reputation: 167

Mock File, FileReader and BufferedReader class using Mockito

I got below code in a method which I want to test

File f = map.get("key1")
BuffereReader r = new BufferedReader(new FileReader(f));
String line=null;
do {
    line=r.readLine();
} while(r!=null);

I want to mock this operation so that I can pass the content of the file from the JUnit test case. I have done below:

Map fles = Mockito.mock(ConcurrentHashMap.class);
File file = Mockito.mock(File.class);
Mockito.when(files.get("key1")).thenReturn(file);

FileReader fileReader = Mockito.mock(FileReader.class);
BufferedReader bufferedReader = Mockito.mock(BufferedReader.class);

try {
     PowerMockito.whenNew(FileReader.class).withArguments(file).thenReturn(fileReader);
     PowerMockito.whenNew(BufferedReader.class).withArguments(fileReader).thenReturn(bufferedReader);
     PowerMockito.when(bufferedReader.readLine()).thenReturn("line1")
         .thenReturn("line2").thenReturn("line3");

    } catch (Exception e) {
        Assert.fail();
    }

So basically I need to pass "line1", "line2" and "line3" as lines from the file which are read by the mocked BufferedReader.

However upon doing that, it failes as NullPointerException when trying to instantiate new FileReader(f) part.

So is it because I can't mock a BufferedReader or the approach is wrong?

Thanks

Upvotes: 10

Views: 39747

Answers (2)

Bobbo
Bobbo

Reputation: 315

You could extract a method for doing the actual reading and then test that instead. That would mean you only have to mock a single reader. For example, your code would be something like this: 

public void aMethod(){
    File f = map.get("key1")
    BuffereReader r = new BufferedReader(new FileReader(f));
    readStuff(r);
}

public void readStuff(BufferedReader r){
    String line=null;
    do {
        line=r.readLine();
    } while(r!=null);
}

then your test code would be more like the following:

BufferedReader bufferedReader = Mockito.mock(BufferedReader.class);
Mockito.when(bufferedReader.readLine()).thenReturn("line1", "line2", "line3");
objUnderTest.readStuff(bufferedReader);
//verify result

Upvotes: 15

Sai
Sai

Reputation: 376

You can try PowerMock annotations. Check this : https://code.google.com/p/powermock/wiki/MockConstructor

Upvotes: 0

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