Remove more or less duplicate test cases for 2in9 buffer

src/epd2in9/graphics.rs

@@ -0,0 +1,41 @@
+use epd2in9::{DEFAULT_BACKGROUND_COLOR, WIDTH, HEIGHT};
+
+pub struct Buffer2in9 {
+    pub buffer: [u8; WIDTH as usize * HEIGHT as usize / 8],
+}
+
+impl Default for Buffer2in9 {
+    fn default() -> Self {
+        Buffer2in9 {
+            buffer: [
+                DEFAULT_BACKGROUND_COLOR.get_byte_value();
+                WIDTH as usize * HEIGHT as usize / 8                
+            ]
+        }
+    }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use graphics::Display;
+
+    // test buffer length
+    #[test]
+    fn graphics_size() {
+        let mut buffer = Buffer2in9::default();
+        let display = Display::new(WIDTH, HEIGHT, &mut buffer.buffer);
+        assert_eq!(display.buffer().len(), 4736);
+    }
+    
+    // test default background color on all bytes
+    #[test]
+    fn graphics_default() {
+        let mut buffer = Buffer2in9::default();
+        let display = Display::new(WIDTH, HEIGHT, &mut buffer.buffer);
+        for &byte in display.buffer() {
+            assert_eq!(byte, DEFAULT_BACKGROUND_COLOR.get_byte_value());
+        }
+    }
+}

src/epd2in9/mod.rs

@@ -39,6 +39,9 @@ use traits::*;
 
 use interface::DisplayInterface;
 
+mod graphics;
+pub use epd2in9::graphics::Buffer2in9;
+
 /// EPD2in9 driver
 ///
 pub struct EPD2in9<SPI, CS, BUSY, DC, RST> {