Improve test for String.intern

We add a version of the test which should fail in addition to the one
that should pass.

Author: romainbrenguier

jbmc/regression/strings-smoke-tests/java_intern/test.desc

@@ -1,8 +1,8 @@
 CORE
 test_intern.class
---max-nondet-string-length 1000 --function test_intern.main --cp `../../../../scripts/format_classpath.sh . ../../../lib/java-models-library/target/core-models.jar` --unwind 10
+--max-nondet-string-length 1000 --function test_intern.testPass --cp `../../../../scripts/format_classpath.sh . ../../../lib/java-models-library/target/core-models.jar` --unwind 10
 ^EXIT=0$
 ^SIGNAL=0$
-^\[.*assertion.1\].* line 9.* SUCCESS$
+^\[.*assertion.1\].* line 12.* SUCCESS$
 --
 non equal types

jbmc/regression/strings-smoke-tests/java_intern/testFail.desc

@@ -0,0 +1,8 @@
+CORE
+test_intern.class
+--max-nondet-string-length 1000 --function test_intern.testFail --cp `../../../../scripts/format_classpath.sh . ../../../lib/java-models-library/target/core-models.jar` --unwind 10
+^EXIT=10$
+^SIGNAL=0$
+^\[.*assertion.1\].* line 24.* FAILURE$
+--
+non equal types

jbmc/regression/strings-smoke-tests/java_intern/test_intern.class

@@ -1,11 +1,26 @@
 public class test_intern
 {
-   public static void main()
-   {
-      String s1 = "abc";
-      String s3 = "abc";
-      String x = s1.intern();
-      String y = s3.intern();
-      assert(x == y);
+    public static void testPass()
+    {
+        // Arrange
+        String s1 = "abc";
+        String s2 = "abc";
+        // Act
+        String x = s1.intern();
+        String y = s2.intern();
+        // Assert
+        assert(x == y);
+    }
+
+    public static void testFail()
+    {
+        // Arrange
+        String s1 = "abc";
+        String s2 = "abd";
+        // Act
+        String x = s1.intern();
+        String y = s2.intern();
+        // Assert
+        assert(x == y);
    }
 }