Fix data size check issue

lib/oled/display/impl/ssd_1306.ex

@@ -138,7 +138,7 @@ defmodule OLED.Display.Impl.SSD1306 do
   end
 
   def display_frame(%__MODULE__{} = state, data, opts) do
-    if data != state.width * state.height / 8 do
+    if byte_size(data) == state.width * state.height / 8 do
       display(%{state | buffer: data}, opts)
     else
       {:error, :invalid_data_size}

test/oled/display/impl/ssd_1306_test.exs

@@ -14,4 +14,43 @@ defmodule OLED.Display.Impl.SSD1306Test do
     assert_received {:command, 2}
     assert_received {:command, 3}
   end
+
+  describe "display_frame/2" do
+    test "with valid data" do
+      state = %SSD1306{
+        dev: %DummyDev{},
+        width: 96,
+        height: 48
+      }
+
+      data =
+        for _ <- 1..576, into: <<>> do
+          <<0>>
+        end
+
+      assert %SSD1306{} = SSD1306.display_frame(state, data, memory_mode: :vertical)
+
+      assert_received {:command, 32}
+      assert_received {:command, 1}
+      assert_received {:transfer, ^data}
+      assert_received {:command, 32}
+      assert_received {:command, 0}
+    end
+
+    test "with invalid data" do
+      state = %SSD1306{
+        dev: %DummyDev{},
+        width: 96,
+        height: 48
+      }
+
+      data =
+        for _ <- 1..200, into: <<>> do
+          <<0>>
+        end
+
+      assert {:error, :invalid_data_size} =
+               SSD1306.display_frame(state, data, memory_mode: :vertical)
+    end
+  end
 end

test/support/dummy_dev.ex

@@ -10,20 +10,20 @@ defmodule OLED.DummyDev do
   end
 
   @impl true
-  def reset(%__MODULE__{}) do
+  def reset(%__MODULE__{} = state) do
     send(self(), :reset)
-    %__MODULE__{}
+    state
   end
 
   @impl true
-  def transfer(%__MODULE__{}, buffer) do
+  def transfer(%__MODULE__{} = state, buffer) do
     send(self(), {:transfer, buffer})
-    %__MODULE__{}
+    state
   end
 
   @impl true
-  def command(%__MODULE__{}, cmd) do
+  def command(%__MODULE__{} = state, cmd) do
     send(self(), {:command, cmd})
-    %__MODULE__{}
+    state
   end
 end