Comparing text files with Junit

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.

junit-addons has nice support for it: FileAssert

It gives you exceptions like:

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

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

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.

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());
}