Incomplete `expected` is created for classes from Java standard library

[IlyaMuravjov]

Description

No fields of expected are set, leading to equals overridden equals returning false or crashing and assertEquals(expected, actual) failing.

To Reproduce

Generate tests for the following class

public class JavaUtils {
    public static Date getEpochStart() {
        return Date.from(Instant.EPOCH);
    }

    public static File getSomeFile() {
        return new File("file.txt");
    }

    public static BigInteger getSomeBigInteger() {
        return BigInteger.ZERO;
    }
}

Expected behavior

One passing test per method.

Actual behavior

One failing (at runtime) test per method.

public final class JavaUtilsTest {
    ///region Test suites for executable org.example.JavaUtils.getEpochStart

    ///region SYMBOLIC EXECUTION: SUCCESSFUL EXECUTIONS for method getEpochStart()

    /**
     * @utbot.classUnderTest {@link JavaUtils}
     * @utbot.methodUnderTest {@link JavaUtils#getEpochStart()}
     * @utbot.invokes {@link Date#from(java.time.Instant)}
     */
    @Test
    @DisplayName("getEpochStart: -> DateFrom")
    public void testGetEpochStart_DateFrom() {
        Date actual = JavaUtils.getEpochStart();

        Date expected = new Date();

        // java.util.Date has overridden equals method
        assertEquals(expected, actual);
    }
    ///endregion

    ///endregion

    ///region Test suites for executable org.example.JavaUtils.getSomeBigInteger

    ///region SYMBOLIC EXECUTION: SUCCESSFUL EXECUTIONS for method getSomeBigInteger()

    /**
     * @utbot.classUnderTest {@link JavaUtils}
     * @utbot.methodUnderTest {@link JavaUtils#getSomeBigInteger()}
     * @utbot.returnsFrom {@code return BigInteger.ZERO;}
     */
    @Test
    @DisplayName("getSomeBigInteger: -> return BigInteger.ZERO")
    public void testGetSomeBigInteger_ReturnBigIntegerZERO() throws Exception {
        BigInteger actual = JavaUtils.getSomeBigInteger();

        BigInteger expected = ((BigInteger) createInstance("java.math.BigInteger"));

        // java.math.BigInteger has overridden equals method
        assertEquals(expected, actual);
    }
    ///endregion

    ///endregion

    ///region Test suites for executable org.example.JavaUtils.getSomeFile

    ///region OTHER: SUCCESSFUL EXECUTIONS for method getSomeFile()

    @Test
    public void testGetSomeFile1() throws Exception {
        File actual = JavaUtils.getSomeFile();

        File expected = ((File) createInstance("java.io.File"));

        // java.io.File has overridden equals method
        assertEquals(expected, actual);
    }
    ///endregion

    ///endregion
}

Errors:

org.opentest4j.AssertionFailedError: expected: <Thu Aug 31 15:45:57 MSK 2023> but was: <Thu Jan 01 03:00:00 MSK 1970>
	at org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:151)
	at org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
	at org.junit.jupiter.api.AssertEquals.failNotEqual(AssertEquals.java:197)
	at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:182)
	at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
	at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1142)
	at org.example.JavaUtilsTest.testGetEpochStart_DateFrom(JavaUtilsTest.java:31)

java.lang.NullPointerException
	at java.base/java.io.WinNTFileSystem.compare(WinNTFileSystem.java:698)
	at java.base/java.io.File.compareTo(File.java:2198)
	at java.base/java.io.File.equals(File.java:2217)
	at org.junit.jupiter.api.AssertionUtils.objectsAreEqual(AssertionUtils.java:110)
	at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:181)
	at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
	at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1142)
	at org.example.JavaUtilsTest.testGetSomeFile1(JavaUtilsTest.java:71)

java.lang.NullPointerException
	at java.base/java.math.BigInteger.equals(BigInteger.java:3865)
	at org.junit.jupiter.api.AssertionUtils.objectsAreEqual(AssertionUtils.java:110)
	at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:181)
	at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
	at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1142)
	at org.example.JavaUtilsTest.testGetSomeBigInteger_ReturnBigIntegerZERO(JavaUtilsTest.java:54)

[IlyaMuravjov]

It's unclear what exactly we want to achieve here. If we set all fields, that may over inflate models and generated tests.

Quick fix:

• mark models that have missing fields (including missing fields of fields, etc.)
• don’t use overwritten equals() for such models (only compare fields that are present in the model)

Optional step:

• instead of not constructing models for Java standard library classes, limit max model construction depth for these classes to like 1-3 layers

[alisevych]

Additional context

The issue is reproducing in spring-petclinic project in a test on VisitController$loadPetWithVisit method.
Actual date LocalDate.now()
Expected is ((LocalDate) createInstance("java.time.LocalDate"));

So assert fails with error

expected: <0000-00-00> but was: <2023-09-18>

[tyuldashev]

Is it different from #94 (The engine can not handle some JDK APIs，e.g., Date) problem?

[alisevych]

Is it different from #94 (The engine can not handle some JDK APIs，e.g., Date) problem?

Yes, it's a different issue.
This issue is regarding how instrumented process is creating classes. And then the model is applied in tests as the expected result of concrete execution.
While #94 is regarding symbolic engine limitations.