Fix isDataClassEqualTo not working with data objects (#552)

* fix `isDataClassEqualTo` not working with `data object`s

assertk/src/jvmMain/kotlin/assertk/assertions/any.kt

@@ -82,7 +82,7 @@ fun <T : Any> Assert<T>.isDataClassEqualTo(expected: T) = given { actual ->
 
 private fun <T> Assert<T>.isDataClassEqualToImpl(expected: T, kclass: KClass<*>?): Unit = given { actual ->
     if (actual == expected) return
-    val compareProps = actual != null && expected != null
+    val compareProps = actual != null && expected?.let { it::class } == kclass
     if (compareProps && kclass != null && kclass.isData) {
         for (memberProp in kclass.memberProperties) {
             @Suppress("UNCHECKED_CAST")

assertk/src/jvmTest/kotlin/test/assertk/assertions/JavaAnyTest.kt

@@ -111,6 +111,11 @@ class JavaAnyTest {
             .isDataClassEqualTo(DataClass(InnerDataClass("test"), 1, 'a'))
     }
 
+    @Test
+    fun isDataClassEqualTo_equal_data_objects_passes() {
+        assertThat(DataObject).isDataClassEqualTo(DataObject)
+    }
+
     @Test
     fun isDataClassEqualTo_reports_all_properties_that_differ_on_failure() {
         val error = assertFailsWith<AssertionError> {
@@ -152,6 +157,17 @@ class JavaAnyTest {
         """.trimMargin().lines(), error.message!!.lines()
         )
     }
+
+    @Test
+    fun isDataClassEqualTo_fails_different_data_objects() {
+        val error = assertFailsWith<AssertionError> {
+            assertThat(DataObject).isDataClassEqualTo(OtherDataObject)
+        }
+        assertEquals(
+            "expected:<[Other]DataObject> but was:<[]DataObject>"
+                .lines(), error.message!!.lines()
+        )
+    }
     //endregion
 
     //region isEqualToIgnoringGivenProperties
@@ -217,5 +233,9 @@ class JavaAnyTest {
     data class DataClass(val one: InnerDataClass?, val two: Int, val three: Char)
 
     data class InnerDataClass(val inner: String)
+
+    data object DataObject
+
+    data object OtherDataObject
 }