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2 ScalaCheck versus JUnit: A Complete Example

2.1 The class under test

import java.util.StringTokenizer;

public class StringUtils {

  public static String truncate(String s, int n) {
    if(s.length() <= n) return s;
    else return s.substring(0, n) + "...";
  }

  public static String[] tokenize(
    String s, char delim
  ) {
    String delimStr = new Character(delim).toString();
    StringTokenizer st = new StringTokenizer(
      s, delimStr);
    String[] tokens = new String[st.countTokens()];
    int i = 0;
    while(st.hasMoreTokens()) {
      tokens[i] = st.nextToken();
      i++;
    }
    return tokens;
  }

  public static boolean contains(
    String s, String subString
  ) {
    return s.indexOf(subString) != -1;
  }

}


  

2.2 Using JUnit

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.assertFalse;

@RunWith(JUnit4.class)
public class StringUtilsTest {
  @Test public void testTruncateShortString() {
    String s = StringUtils.truncate("abc", 5);
    assertEquals("abc", s);
  }
  @Test public void testTruncateLongString() {
    String s = StringUtils.truncate("Hello World", 8);
    assertEquals("Hello Wo...", s);
  }
  @Test public void testTokenize() {
    String[] tokens = StringUtils.tokenize(
      "foo;bar;42", ';');
    String[] expected = { "foo", "bar", "42" };
    assertTrue(java.util.Arrays.equals(tokens, expected));
  }
  @Test public void testTokenizeSingle() {
    String[] tokens = StringUtils.tokenize(
      "Hello World", ',');
    String[] expected = { "Hello World" };
    assertTrue(java.util.Arrays.equals(tokens, expected));
  }
  @Test public void testContainsTrue() {
    assertTrue(StringUtils.contains("abc", "bc"));
  }
  @Test public void testContainsFalse() {
    assertFalse(StringUtils.contains("abc", "42"));
  }
}


$ javac -cp junit-4.11.jar \
  StringUtils.java StringUtilsTest.java
$ java -cp .:junit-4.11.jar:hamcrest-core-1.3.jar \
  org.junit.runner.JUnitCore StringUtilsTest
JUnit version 4.11
......
Time: 0.006

OK (6 tests)


  

2.3 Using ScalaCheck

import org.scalacheck.Properties
import org.scalacheck.Prop
import org.scalacheck.Gen.{listOf, alphaStr, numChar}

object StringUtilsProps extends
  Properties("StringUtils")
{
  property("truncate") =
    Prop.forAll { (s: String, n: Int) =>
      val t = StringUtils.truncate(s, n)
      (s.length <= n && t == s) ||
      (s.length > n && t == s.take(n)+"...")
    }

  property("tokenize") =
    Prop.forAll(listOf(alphaStr), numChar) {
      (ts, d) =>
        val str = ts.mkString(d.toString)
        StringUtils.tokenize(str, d).toList == ts
    }

  property("contains") = Prop.forAll {
    (s1: String, s2: String, s3: String) =>
      StringUtils.contains(s1+s2+s3, s2)
  }
}


 $ javac StringUtils.java
 $ scalac -cp .:scalacheck.jar StringUtilProps.scala
 $ scala -cp .:scalacheck.jar StringUtilProps
 ! StringUtils.truncate: Exception raised on property
 evaluation.
 > ARG_0: ""
 > ARG_1: -1
 > ARG_1_ORIGINAL: -1110151355
 > Exception: java.lang.StringIndexOutOfBoundsException:
 String index out of range: -1
 java.lang.String.substring(String.java:1911)
 StringUtils.truncate(StringUtils.java:7)
 StringUtilsProps$$anonfun$1.apply(StringUtilsProps.scala:9)
 StringUtilsProps$$anonfun$1.apply(StringUtilsProps.scala:8)
 org.scalacheck.Prop$$anonfun$forAll$10$$anonfun$apply$25
 .apply(Prop.scala:759)
 ! StringUtils.tokenize: Falsified after 5 passed tests.
 > ARG_0: List("")
 > ARG_0_ORIGINAL: List("", "yHa", "vlez", "Oyex", "lhz")
 > ARG_1: 2
 + StringUtils.contains: OK, passed 100 tests.


property("truncate") =
  Prop.forAll { (s: String, n: Int) =>
    lazy val t = StringUtils.truncate(s, n)
    if (n < 0)
      Prop.throws(
        classOf[StringIndexOutOfBoundsException]
      ) { t }
    else
      (s.length <= n && t == s) ||
      (s.length > n && t == s.take(n)+"...")
  }


import Prop.BooleanOperators

property("truncate") =
  Prop.forAll { (s: String, n: Int) =>
    (n >= 0) ==> {
      val t = StringUtils.truncate(s, n)
      (s.length <= n && t == s) ||
      (s.length > n && t == s.take(n)+"...")
    }
  }


public static String truncate(String s, int n) {
  if(n < 0) return "";
  else if(s.length() <= n) return s;
  else return s.substring(0, n) + "...";
}


property("truncate") =
  Prop.forAll { (s: String, n: Int) =>
    val t = StringUtils.truncate(s, n)
    if(n < 0) t == ""
    else
      (s.length <= n && t == s) ||
      (s.length > n && t == s.take(n)+"...")
  }


$ scala -cp .:scalacheck.jar StringUtilProps
 + StringUtils.truncate: OK, passed 100 tests.
 ! StringUtils.tokenize: Falsified after 3 passed tests.
 > ARG_0: List("")
 > ARG_0_ORIGINAL: List("", "")
 > ARG_1: 9
 + StringUtils.contains: OK, passed 100 tests.


property("tokenize") = {
  import Prop.AnyOperators
  Prop.forAll(listOf(alphaStr), numChar) { (ts, d) =>
    val str = ts.mkString(d.toString)
    StringUtils.tokenize(str, d).toList ?= ts
  }
}


$ scala -cp .:scalacheck.jar StringUtilProps
 + StringUtils.truncate: OK, passed 100 tests.
 ! StringUtils.tokenize: Falsified after 3 passed tests.
 > Labels of failing property:
 Expected List("") but got List()
 > ARG_0: List("")
 > ARG_0_ORIGINAL: List("", "E", "zd")
 > ARG_1: 4
 + StringUtils.contains: OK, passed 100 tests.


  

2.4 Conclusion