diff --git a/matrix-chat-engine/src/test/kotlin/app/dapk/st/engine/SendMessageUseCaseTest.kt b/matrix-chat-engine/src/test/kotlin/app/dapk/st/engine/SendMessageUseCaseTest.kt
new file mode 100644
index 0000000..f675c92
--- /dev/null
+++ b/matrix-chat-engine/src/test/kotlin/app/dapk/st/engine/SendMessageUseCaseTest.kt
@@ -0,0 +1,139 @@
+package app.dapk.st.engine
+
+import app.dapk.st.matrix.common.RichText
+import app.dapk.st.matrix.message.MessageService
+import app.dapk.st.matrix.message.internal.ImageContentReader
+import fake.FakeLocalIdFactory
+import fixture.aRoomMember
+import fixture.aRoomOverview
+import fixture.anEventId
+import io.mockk.every
+import io.mockk.mockk
+import org.junit.Test
+import test.delegateReturn
+import test.runExpectTest
+import java.time.Clock
+
+private const val AN_IMAGE_URI = ""
+private val AN_IMAGE_META = ImageContentReader.ImageContent(
+    height = 50,
+    width = 100,
+    size = 1000L,
+    fileName = "a file name",
+    mimeType = "image/png"
+)
+private const val A_CURRENT_TIME = 2000L
+private const val A_LOCAL_ID = "a local id"
+private val A_ROOM_OVERVIEW = aRoomOverview(
+    isEncrypted = true
+)
+private val A_REPLY = SendMessage.TextMessage.Reply(
+    aRoomMember(),
+    originalMessage = "",
+    anEventId(),
+    timestampUtc = 7000
+)
+private const val A_TEXT_MESSAGE_CONTENT = "message content"
+
+class SendMessageUseCaseTest {
+
+    private val fakeMessageService = FakeMessageService()
+    private val fakeLocalIdFactory = FakeLocalIdFactory().apply { givenCreate().returns(A_LOCAL_ID) }
+    private val fakeImageContentReader = FakeImageContentReader()
+    private val fakeClock = FakeClock().apply { givenMillis().returns(A_CURRENT_TIME) }
+
+    private val useCase = SendMessageUseCase(
+        fakeMessageService,
+        fakeLocalIdFactory.instance,
+        fakeImageContentReader,
+        fakeClock.instance
+    )
+
+    @Test
+    fun `when sending image message, then schedules message`() = runExpectTest {
+        fakeImageContentReader.givenMeta(AN_IMAGE_URI).returns(AN_IMAGE_META)
+        val expectedImageMessage = createExpectedImageMessage(A_ROOM_OVERVIEW)
+        fakeMessageService.expect { it.scheduleMessage(expectedImageMessage) }
+
+        useCase.send(SendMessage.ImageMessage(uri = AN_IMAGE_URI), A_ROOM_OVERVIEW)
+
+        verifyExpects()
+    }
+
+    @Test
+    fun `when sending text message, then schedules message`() = runExpectTest {
+        val expectedTextMessage = createExpectedTextMessage(A_ROOM_OVERVIEW, A_TEXT_MESSAGE_CONTENT, reply = null)
+        fakeMessageService.expect { it.scheduleMessage(expectedTextMessage) }
+
+        useCase.send(
+            SendMessage.TextMessage(
+                content = A_TEXT_MESSAGE_CONTENT,
+                reply = null,
+            ),
+            A_ROOM_OVERVIEW
+        )
+
+        verifyExpects()
+    }
+
+    @Test
+    fun `given a reply, when sending text message, then schedules message with reply`() = runExpectTest {
+        val expectedTextMessage = createExpectedTextMessage(A_ROOM_OVERVIEW, A_TEXT_MESSAGE_CONTENT, reply = A_REPLY)
+        fakeMessageService.expect { it.scheduleMessage(expectedTextMessage) }
+
+        useCase.send(
+            SendMessage.TextMessage(
+                content = A_TEXT_MESSAGE_CONTENT,
+                reply = A_REPLY,
+            ),
+            A_ROOM_OVERVIEW
+        )
+
+        verifyExpects()
+    }
+
+
+    private fun createExpectedImageMessage(roomOverview: RoomOverview) = MessageService.Message.ImageMessage(
+        MessageService.Message.Content.ImageContent(
+            uri = AN_IMAGE_URI,
+            MessageService.Message.Content.ImageContent.Meta(
+                height = AN_IMAGE_META.height,
+                width = AN_IMAGE_META.width,
+                size = AN_IMAGE_META.size,
+                fileName = AN_IMAGE_META.fileName,
+                mimeType = AN_IMAGE_META.mimeType,
+            )
+        ),
+        roomId = roomOverview.roomId,
+        sendEncrypted = roomOverview.isEncrypted,
+        localId = A_LOCAL_ID,
+        timestampUtc = A_CURRENT_TIME,
+    )
+
+    private fun createExpectedTextMessage(roomOverview: RoomOverview, messageContent: String, reply: SendMessage.TextMessage.Reply?) =
+        MessageService.Message.TextMessage(
+            content = MessageService.Message.Content.TextContent(RichText.of(messageContent)),
+            roomId = roomOverview.roomId,
+            sendEncrypted = roomOverview.isEncrypted,
+            localId = A_LOCAL_ID,
+            timestampUtc = A_CURRENT_TIME,
+            reply = reply?.let {
+                MessageService.Message.TextMessage.Reply(
+                    author = it.author,
+                    originalMessage = RichText.of(it.originalMessage),
+                    replyContent = messageContent,
+                    eventId = it.eventId,
+                    timestampUtc = it.timestampUtc,
+                )
+            }
+        )
+}
+
+class FakeImageContentReader : ImageContentReader by mockk() {
+    fun givenMeta(uri: String) = every { meta(uri) }.delegateReturn()
+}
+
+class FakeClock {
+    val instance = mockk<Clock>()
+    fun givenMillis() = every { instance.millis() }.delegateReturn()
+}