Rollback the removed tests

Author: yevhenii-nadtochii

java-tests/runtime/src/test/kotlin/io/spine/validate/EntityIdSpec.kt

@@ -44,10 +44,72 @@ import org.junit.jupiter.api.assertDoesNotThrow
 @DisplayName(VALIDATION_SHOULD + "validate an entity ID")
 internal class EntityIdSpec : ValidationOfConstraintTest() {
 
+    @Nested inner class
+    `in a command file and` {
+
+        @Test
+        fun `find out that non-default message is valid`() {
+            val state = assertDoesNotThrow {
+                entityIdMsgFieldValue {
+                    value = newStringValue()
+                }
+            }
+            assertValid(state)
+        }
+
+        @Test
+        fun `find out that default message is NOT valid`() {
+            val msg = EntityIdMsgFieldValue.getDefaultInstance()
+            assertNotValid(msg)
+        }
+
         @Test
         fun `find out that empty string is NOT valid`() {
             val msg = EntityIdStringFieldValue.getDefaultInstance()
             assertNotValid(msg)
         }
 
+        @Test
+        fun `find out that non-empty string is valid`() {
+            val state = assertDoesNotThrow {
+                entityIdStringFieldValue {
+                    value = Identifier.newUuid()
+                }
+            }
+            assertValid(state)
+        }
+
+        @Test
+        fun `provide a violation if is not valid`() {
+            val msg = EntityIdMsgFieldValue.getDefaultInstance()
+            assertSingleViolation(msg, MessageValidatorTestEnv.VALUE)
+        }
+    }
+
+    @Nested inner class
+    `in a state and` {
+
+        @Test
+        fun `consider it required by default`() {
+            val stateWithDefaultId = AggregateState.getDefaultInstance()
+            assertNotValid(stateWithDefaultId)
+        }
+
+        @Test
+        fun `match only the first field named 'id' or ending with '_id'`() {
+            val onlyEntityIdSet = assertDoesNotThrow {
+                // Only ID set.
+                aggregateState {
+                    entityId = Identifier.newUuid()
+                }
+            }
+            assertValid(onlyEntityIdSet)
+        }
+
+        @Test
+        fun `not consider it '(required)' if the option is set explicitly to false`() {
+            val stateWithDefaultId = ProjectionState.getDefaultInstance()
+            assertValid(stateWithDefaultId)
+        }
+    }
 }