Comparing text files with Junit

Question

I am comparing text files in junit using:

public static void assertReaders(BufferedReader expected,
          BufferedReader actual) throws IOException {
    String line;
    while ((line = expected.readLine()) != null) {
        assertEquals(line, actual.readLine());
    }

    assertNull("Actual had more lines then the expected.", actual.readLine());
    assertNull("Expected had more lines then the actual.", expected.readLine());
}

Is this a good way to compare text files? What is preferred?

I'm giving an upvote for the solution you have in the question. Since this is an older post, JUnit add ons is out of date (probably not compatible with JUnit 4), I don't like Apache Utils and given how concise your assertReaders method is I don't see justification for including a whole new library of utilities. Yours worked right off the bat - thanks! — PMorganCA, Apr 17 '20 at 18:21

score 52 · Answer 1 · edited May 23 '17 at 11:54

52

Here's one simple approach for checking if the files are exactly the same:

assertEquals("The files differ!", 
    FileUtils.readFileToString(file1, "utf-8"), 
    FileUtils.readFileToString(file2, "utf-8"));

Where file1 and file2 are File instances, and FileUtils is from Apache Commons IO.

Not much own code for you to maintain, which is always a plus. :) And very easy if you already happen to use Apache Commons in your project. But no nice, detailed error messages like in mark's solution.

Edit:
Heh, looking closer at the FileUtils API, there's an even simpler way:

assertTrue("The files differ!", FileUtils.contentEquals(file1, file2));

As a bonus, this version works for all files, not just text.

edited May 23 '17 at 11:54

Community

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answered Jan 21 '09 at 21:32

Jonik

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The assertTrue form is concise, but relatively useless when it fails. At least the assertEquals method will show you a few characters where they are different – Stephen Jun 10 '10 at 10:33
3

**Update**: Nowadays I'd recommend [Google Guava](http://code.google.com/p/guava-libraries/) over Commons IO for reading the files as string: `Files.toString(file1, Charset.forName("UTF-8"));` There isn't much difference in a case like this, but overall Guava is a cleaner, better documented and actively maintained library. – Jonik Jul 18 '11 at 18:12
6

And since **Java 7** you can [read a text file as string](http://stackoverflow.com/a/326440/56285) quite simply without any external libs: `new String(Files.readAllBytes(Paths.get("/path/to/file.txt")), StandardCharsets.UTF_8)` – Jonik Dec 24 '15 at 01:31

score 31 · Accepted Answer · edited Jun 16 '14 at 12:44

31

junit-addons has nice support for it: FileAssert

It gives you exceptions like:

junitx.framework.ComparisonFailure: aa Line [3] expected: [b] but was:[a]

edited Jun 16 '14 at 12:44

Uooo

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answered Jan 21 '09 at 20:36

IAdapter

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Just a note the latest version vin maven central repo is from 2003 and version 1.4 so i don't know if its compatible with the latest versions. – kohlerfc Nov 19 '15 at 21:00

score 27 · Answer 3 · edited Mar 15 '15 at 16:27

27

Here is a more exhaustive list of File comparator's in various 3rd-party Java libraries:

edited Mar 15 '15 at 16:27

Bogdan Calmac

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answered Jun 09 '10 at 01:18

Scott Langley

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Sweet overview! Spared me the websearch if spring has something included ;) – JBA Apr 14 '15 at 10:44

score 21 · Answer 4 · edited Aug 18 '22 at 13:42

As of 2015, I would recomment AssertJ, an elegant and comprehensive assertion library. For files, you can assert against another file:

@Test
public void file() {
    File actualFile = new File("actual.txt");
    File expectedFile = new File("expected.txt");
    assertThat(actualFile).hasSameTextualContentAs(expectedFile);
}

or against inline strings:

@Test
public void inline() {
    File actualFile = new File("actual.txt");
    assertThat(linesOf(actualFile)).containsExactly(
            "foo 1",
            "foo 2",
            "foo 3"
    );
}

The failure messages are very informative as well. If a line is different, you get:

java.lang.AssertionError: 
File:
  <actual.txt>
and file:
  <expected.txt>
do not have equal content:
line:<2>, 
Expected :foo 2
Actual   :foo 20

and if one of the files has more lines you get:

java.lang.AssertionError:
File:
  <actual.txt>
and file:
  <expected.txt>
do not have equal content:
line:<4>,
Expected :EOF
Actual   :foo 4

The method `hasContentEqualTo` is deprecated as of this comment. Use `hasSameContentAs` instead. — Stephan, Feb 01 '17 at 00:44

score 11 · Answer 5 · edited Dec 22 '19 at 19:39

Simple comparison of the content of two files with java.nio.file API.

byte[] file1Bytes = Files.readAllBytes(Paths.get("Path to File 1"));
byte[] file2Bytes = Files.readAllBytes(Paths.get("Path to File 2"));

String file1 = new String(file1Bytes, StandardCharsets.UTF_8);
String file2 = new String(file2Bytes, StandardCharsets.UTF_8);

assertEquals("The content in the strings should match", file1, file2);

Or if you want to compare individual lines:

List<String> file1 = Files.readAllLines(Paths.get("Path to File 1"));
List<String> file2 = Files.readAllLines(Paths.get("Path to File 2"));

assertEquals(file1.size(), file2.size());

for(int i = 0; i < file1.size(); i++) {
   System.out.println("Comparing line: " + i)
   assertEquals(file1.get(i), file2.get(i));
}

score 7 · Answer 6 · answered Jan 21 '09 at 21:01

I'd suggest using Assert.assertThat and a hamcrest matcher (junit 4.5 or later - perhaps even 4.4).

I'd end up with something like:

assertThat(fileUnderTest, containsExactText(expectedFile));

where my matcher is:

class FileMatcher {
   static Matcher<File> containsExactText(File expectedFile){
      return new TypeSafeMatcher<File>(){
         String failure;
         public boolean matchesSafely(File underTest){
            //create readers for each/convert to strings
            //Your implementation here, something like:
              String line;
              while ((line = expected.readLine()) != null) {
                 Matcher<?> equalsMatcher = CoreMatchers.equalTo(line);
                 String actualLine = actual.readLine();
                 if (!equalsMatcher.matches(actualLine){
                    failure = equalsMatcher.describeFailure(actualLine);
                    return false;
                 }
              }
              //record failures for uneven lines
         }

         public String describeFailure(File underTest);
             return failure;
         }
      }
   }
}

Matcher pros:

Composition and reuse
Use in normal code as well as test
- Collections
- Used in mock framework(s)
- Can be used a general predicate function
Really nice log-ability
Can be combined with other matchers and descriptions and failure descriptions are accurate and precise

Cons:

Well it's pretty obvious right? This is way more verbose than assert or junitx (for this particular case)
You'll probably need to include the hamcrest libs to get the most benefit

score 5 · Answer 7 · answered Jan 13 '11 at 18:15

5

FileUtils sure is a good one. Here's yet another simple approach for checking if the files are exactly the same.

assertEquals(FileUtils.checksumCRC32(file1), FileUtils.checksumCRC32(file2));

While the assertEquals() does provide a little more feedback than the assertTrue(), the result of checksumCRC32() is a long. So, that may not be intrisically helpful.

answered Jan 13 '11 at 18:15

Mookie Wilson

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+1, I guess this could come in handy for really large files (when you only care about whether the files differ, not what the difference is) – Jonik Jul 26 '11 at 16:52

Jon Skeet · Answer 8 · 2014-01-31T20:32:21.927

4

If expected has more lines than actual, you'll fail an assertEquals before getting to the assertNull later.

It's fairly easy to fix though:

public static void assertReaders(BufferedReader expected,
    BufferedReader actual) throws IOException {
  String expectedLine;
  while ((expectedLine = expected.readLine()) != null) {
    String actualLine = actual.readLine();
    assertNotNull("Expected had more lines then the actual.", actualLine);
    assertEquals(expectedLine, actualLine);
  }
  assertNull("Actual had more lines then the expected.", actual.readLine());
}

edited Jan 31 '14 at 20:32

answered Jan 21 '09 at 20:31

Jon Skeet

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I like that your answer doesn't rely on any third party libraries but this code won't compile. The scope of the variable 'actual' is limited to the while-loop so the final assertNull line won't compile. – buzz3791 Jan 31 '14 at 20:30
@buzz3791: No, the scope of `actualLine` is limited to the while loop. The scope of `actual` is the whole method. – Jon Skeet Jan 31 '14 at 20:32

score 0 · Answer 9 · answered Jun 07 '15 at 05:29

This is my own implementation of equalFiles, no need to add any library to your project.

private static boolean equalFiles(String expectedFileName,
        String resultFileName) {
    boolean equal;
    BufferedReader bExp;
    BufferedReader bRes;
    String expLine ;
    String resLine ;

    equal = false;
    bExp = null ;
    bRes = null ;

    try {
        bExp = new BufferedReader(new FileReader(expectedFileName));
        bRes = new BufferedReader(new FileReader(resultFileName));

        if ((bExp != null) && (bRes != null)) {
            expLine = bExp.readLine() ;
            resLine = bRes.readLine() ;

            equal = ((expLine == null) && (resLine == null)) || ((expLine != null) && expLine.equals(resLine)) ;

            while(equal && expLine != null)
            {
                expLine = bExp.readLine() ;
                resLine = bRes.readLine() ; 
                equal = expLine.equals(resLine) ;
            }
        }
    } catch (Exception e) {

    } finally {
        try {
            if (bExp != null) {
                bExp.close();
            }
            if (bRes != null) {
                bRes.close();
            }
        } catch (Exception e) {
        }

    }

    return equal;

}

And to use it just use regular AssertTrue JUnit method

assertTrue(equalFiles(expected, output)) ;

Comparing text files with Junit

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