update AccountService with getById

src/test/kotlin/ltd/lulz/service/AccountServiceTest.kt

@@ -50,4 +50,23 @@ class AccountServiceTest {
 
         verify { repository.save(any()) }
     }
+
+    @Test
+    fun `get by id`() {
+        // given
+        val capture = slot<UUID>()
+        every { repository.findById(capture(capture)) }
+            .answers { Mono.just(AccountEntity(capture.captured, name, amount)) }
+
+        // when stepped
+        StepVerifier.create(service.getById(uuid))
+            .assertNext { result ->
+                assertThat(result.id).isEqualTo(uuid)
+                assertThat(result.name).isEqualTo(name)
+                assertThat(result.amount).isEqualTo(amount)
+            }
+            .verifyComplete()
+
+        verify { repository.findById(any(UUID::class)) }
+    }
 }