@Test
fun serializeTest() {
    @Serializable
    data class Data(val a: Int, val b: String)

    val obj: Data = Json.decodeFromString("""{"a":42, "b": "str"}""")
    assertEquals(42, obj.a)
}

SerializationException: Serializer for class 'Data' is not found.
Please ensure that class is marked as '@Serializable' and that the serialization compiler plugin is applied.

On Kotlin/JS explicitly declared serializer should be used for interfaces and enums without @Serializable annotation
SerializationException: Serializer for class 'Data' is not found.
Please ensure that class is marked as '@Serializable' and that the serialization compiler plugin is applied.

Json.decodeFromString(Data.serializer(), """{"a":42, "b": "str"}""")

kotlin("plugin.serialization") version "1.8.10"
implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.5.0")