Add test to verify TemporalAccessor serialization. (#638)

* Add test to verify TemporalAccessor serialization.

* mark test as PendingFeature

cache-core/src/test/groovy/io/micronaut/cache/serialize/DefaultStringKeySerializerSpec.groovy

@@ -0,0 +1,39 @@
+package io.micronaut.cache.serialize
+
+import io.micronaut.core.convert.DefaultMutableConversionService
+import spock.lang.Issue
+import spock.lang.PendingFeature
+import spock.lang.Specification
+
+import java.nio.charset.Charset
+import java.time.LocalDate
+import java.time.LocalDateTime
+import java.time.OffsetDateTime
+import java.time.OffsetTime
+import java.time.ZoneId
+import java.time.ZoneOffset
+import java.time.ZonedDateTime
+
+class DefaultStringKeySerializerSpec extends Specification {
+
+    @PendingFeature(reason = "Depends on https://github.com/micronaut-projects/micronaut-core/pull/8963")
+    @Issue("https://github.com/micronaut-projects/micronaut-cache/issues/404")
+    void "test TemporalAccessor serialization"() {
+
+        given:
+        final serializer = new DefaultStringKeySerializer("cacheName", Charset.defaultCharset(), new DefaultMutableConversionService())
+
+        expect:
+        new String(serializer.serialize(sourceObject).get(), Charset.defaultCharset()) == "cacheName:$result"
+
+        where:
+        sourceObject                                                            | result
+        LocalDate.of(2022, 8, 12)                                               | "2022-08-12"
+        LocalDateTime.of(2022, 8, 12, 12, 19)                                   | "2022-08-12T12:19:00"
+        OffsetTime.of(12, 19, 0, 0, ZoneOffset.ofHours(5))                      | "12:19:00+05:00"
+        OffsetDateTime.of(2022, 8, 12, 12, 19, 0, 0, ZoneOffset.ofHours(5))     | "2022-08-12T12:19:00+05:00"
+        ZonedDateTime.of(2022, 8, 12, 12, 19, 0, 0, ZoneOffset.ofHours(5))      | "2022-08-12T12:19:00+05:00"
+        ZonedDateTime.of(2022, 8, 12, 12, 19, 0, 0, ZoneId.of("Europe/Berlin")) | "2022-08-12T12:19:00+02:00[Europe/Berlin]"
+        LocalDateTime.of(2022, 8, 12, 12, 19).toInstant(ZoneOffset.UTC)         | "2022-08-12T12:19:00Z"
+    }
+}