diff --git a/.github/workflows/ci-builds.yml b/.github/workflows/ci-builds.yml
index 271ef03..7cd33d2 100644
--- a/.github/workflows/ci-builds.yml
+++ b/.github/workflows/ci-builds.yml
@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v2
 
       - name: Install Apt Dependencies
-        run: sudo apt-get update && sudo apt-get install binutils-arm-none-eabi
+        run: sudo apt-get update && sudo apt-get install binutils-arm-none-eabi libelf-dev
 
       - uses: actions-rs/toolchain@v1
         with:
@@ -39,3 +39,19 @@ jobs:
           toolchain: ${{ matrix.rust.toolchain }}
           command: check
           args: --no-default-features
+
+      - name: Install mgba-test-runner
+        uses: actions-rs/cargo@v1
+        with:
+          toolchain: ${{ matrix.rust.toolchain }}
+          command: install
+          # newer revisions don't build on aarch64, at least, because of a c_char mishap
+          args: --git https://github.com/agbrs/agb --rev a7f9fdf01118a7a77d4dcf72f2b74a1961458b36 mgba-test-runner
+
+      - name: Run unit tests
+        uses: actions-rs/cargo@v1
+        env:
+          CARGO_TARGET_THUMBV4T_NONE_EABI_RUNNER: mgba-test-runner
+        with:
+          toolchain: ${{ matrix.rust.toolchain }}
+          command: test
diff --git a/src/fixed.rs b/src/fixed.rs
index 3c8aa2a..c4b3ccb 100644
--- a/src/fixed.rs
+++ b/src/fixed.rs
@@ -241,6 +241,24 @@ macro_rules! impl_common_fixed_ops {
         Self(self.0 >> rhs)
       }
     }
+
+    impl<const B: u32> core::fmt::Debug for Fixed<$t, B> {
+      fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        let raw: $t = self.to_bits();
+        write!(
+          f,
+          concat!(
+            "Fixed::<",
+            stringify!($t),
+            ",{}>::from_bits({:#x}_u32 as ",
+            stringify!($t),
+            ")"
+          ),
+          B, raw
+        )
+      }
+    }
+
     impl_trait_op_unit!($t, Not, not);
     impl_trait_op_self_rhs!($t, Add, add);
     impl_trait_op_self_rhs!($t, Sub, sub);
@@ -335,18 +353,13 @@ macro_rules! impl_signed_fixed_ops {
       }
     }
     impl_trait_op_unit!($t, Neg, neg);
-    impl<const B: u32> core::fmt::Debug for Fixed<$t, B> {
-      #[inline]
+
+    impl<const B: u32> core::fmt::Display for Fixed<$t, B> {
       fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
-        let whole: $t = self.trunc().to_bits() >> B;
-        let fract: $t = self.fract().to_bits();
-        let divisor: $t = 1 << B;
-        if self.is_negative() {
-          let whole = whole.unsigned_abs();
-          write!(f, "-({whole}+{fract}/{divisor})")
-        } else {
-          write!(f, "{whole}+{fract}/{divisor}")
+        if self.to_bits() < 0 {
+          f.write_str("-")?;
         }
+        fixed_fmt_abs::<B>(f, self.to_bits().abs() as u32)
       }
     }
   };
@@ -393,13 +406,10 @@ macro_rules! impl_unsigned_fixed_ops {
         Self(self.0 & (<$t>::MAX << B))
       }
     }
-    impl<const B: u32> core::fmt::Debug for Fixed<$t, B> {
-      #[inline]
+
+    impl<const B: u32> core::fmt::Display for Fixed<$t, B> {
       fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
-        let whole: $t = self.trunc().to_bits() >> B;
-        let fract: $t = self.fract().to_bits();
-        let divisor: $t = 1 << B;
-        write!(f, "{whole}+{fract}/{divisor}")
+        fixed_fmt_abs::<B>(f, self.to_bits() as u32)
       }
     }
   };
@@ -407,3 +417,78 @@ macro_rules! impl_unsigned_fixed_ops {
 impl_unsigned_fixed_ops!(u8);
 impl_unsigned_fixed_ops!(u16);
 impl_unsigned_fixed_ops!(u32);
+
+fn fixed_fmt_abs<const B: u32>(
+  f: &mut core::fmt::Formatter, abs: u32,
+) -> core::fmt::Result {
+  let width = f.width().unwrap_or(0);
+  let precision = f.precision().unwrap_or(const { ((B as usize) + 1) / 3 });
+  let fract = abs & ((1 << B) - 1);
+  let fract_dec = 10u32
+    .checked_pow(precision as u32)
+    .and_then(|digits| fract.checked_mul(digits))
+    .map(|x| (x >> B) as u64)
+    .unwrap_or_else(|| (fract as u64 * 10u64.pow(precision as u32) >> B));
+  write!(f, "{:width$}.{:0precision$}", abs >> B, fract_dec)
+}
+
+#[cfg(test)]
+mod test {
+  use crate::fixed::{i16fx14, i32fx8};
+  use core::{fmt::Write, str};
+
+  struct WriteBuf<const N: usize>([u8; N], usize);
+  impl<'a, const N: usize> Default for WriteBuf<N> {
+    fn default() -> Self {
+      Self([0u8; N], 0)
+    }
+  }
+  impl<const N: usize> Write for WriteBuf<N> {
+    fn write_str(&mut self, s: &str) -> core::fmt::Result {
+      let src = s.as_bytes();
+      let len = (self.0.len() - self.1).min(src.len());
+      self.0[self.1..self.1 + len].copy_from_slice(&src[..len]);
+      self.1 += len;
+      if len < src.len() {
+        Err(core::fmt::Error)
+      } else {
+        Ok(())
+      }
+    }
+  }
+  impl<const N: usize> WriteBuf<N> {
+    fn take(&mut self) -> &str {
+      let len = self.1;
+      self.1 = 0;
+      str::from_utf8(&self.0[..len]).unwrap()
+    }
+  }
+
+  #[test_case]
+  fn decimal_display() {
+    let mut wbuf = WriteBuf::<16>::default();
+
+    let x = i32fx8::from_bits(0x12345678);
+
+    write!(&mut wbuf, "{x}").unwrap();
+    assert_eq!(wbuf.take(), "1193046.468");
+
+    write!(&mut wbuf, "{x:9.1}").unwrap();
+    assert_eq!(wbuf.take(), "  1193046.4");
+
+    write!(&mut wbuf, "{x:1.6}").unwrap();
+    assert_eq!(wbuf.take(), "1193046.468750");
+
+    let x = x.neg();
+    write!(&mut wbuf, "{x}").unwrap();
+    assert_eq!(wbuf.take(), "-1193046.468");
+
+    let x = i16fx14::from_bits(0x6544 as i16);
+    write!(&mut wbuf, "{x}").unwrap();
+    assert_eq!(wbuf.take(), "1.58227");
+
+    let x = x.neg();
+    write!(&mut wbuf, "{x:.10}").unwrap();
+    assert_eq!(wbuf.take(), "-1.5822753906");
+  }
+}
diff --git a/src/lib.rs b/src/lib.rs
index e57641f..4263d00 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,6 +5,10 @@
 #![allow(clippy::let_and_return)]
 #![allow(clippy::result_unit_err)]
 #![warn(clippy::missing_inline_in_public_items)]
+#![cfg_attr(test, feature(custom_test_frameworks))]
+#![cfg_attr(test, test_runner(test_harness::test_runner))]
+#![cfg_attr(test, no_main)]
+#![cfg_attr(test, reexport_test_harness_main = "test_main")]
 
 //! A crate for GBA development.
 //!
@@ -174,3 +178,130 @@ macro_rules! include_aligned_bytes {
     Align4(*include_bytes!($file))
   }};
 }
+
+#[cfg(test)]
+mod test_harness {
+  use crate::prelude::*;
+  use crate::{bios, mem, mgba};
+  use core::fmt::Write;
+
+  #[panic_handler]
+  fn panic(info: &core::panic::PanicInfo) -> ! {
+    DISPSTAT.write(DisplayStatus::new().with_irq_vblank(true));
+    BG_PALETTE.index(0).write(Color::from_rgb(25, 10, 5));
+    IE.write(IrqBits::VBLANK);
+    IME.write(true);
+    VBlankIntrWait();
+    VBlankIntrWait();
+    VBlankIntrWait();
+
+    // the Fatal one kills emulation after one line / 256 bytes
+    // so emit all the information as Error first
+    if let Ok(mut log) =
+      mgba::MgbaBufferedLogger::try_new(mgba::MgbaMessageLevel::Error)
+    {
+      writeln!(log, "[failed]").ok();
+      write!(log, "{}", info).ok();
+    }
+
+    if let Ok(mut log) =
+      mgba::MgbaBufferedLogger::try_new(mgba::MgbaMessageLevel::Fatal)
+    {
+      if let Some(loc) = info.location() {
+        write!(log, "panic at {loc}! see mgba error log for details.").ok();
+      } else {
+        write!(log, "panic! see mgba error log for details.").ok();
+      }
+    }
+
+    IE.write(IrqBits::new());
+    bios::IntrWait(true, IrqBits::new());
+    loop {}
+  }
+
+  pub(crate) trait UnitTest {
+    fn run(&self);
+  }
+
+  impl<T: Fn()> UnitTest for T {
+    fn run(&self) {
+      if let Ok(mut log) =
+        mgba::MgbaBufferedLogger::try_new(mgba::MgbaMessageLevel::Info)
+      {
+        write!(log, "{}...", core::any::type_name::<T>()).ok();
+      }
+
+      self();
+
+      if let Ok(mut log) =
+        mgba::MgbaBufferedLogger::try_new(mgba::MgbaMessageLevel::Info)
+      {
+        writeln!(log, "[ok]").ok();
+      }
+    }
+  }
+
+  pub(crate) fn test_runner(tests: &[&dyn UnitTest]) {
+    if let Ok(mut log) =
+      mgba::MgbaBufferedLogger::try_new(mgba::MgbaMessageLevel::Info)
+    {
+      write!(log, "Running {} tests", tests.len()).ok();
+    }
+
+    for test in tests {
+      test.run();
+    }
+    if let Ok(mut log) =
+      mgba::MgbaBufferedLogger::try_new(mgba::MgbaMessageLevel::Info)
+    {
+      write!(log, "Tests finished successfully").ok();
+    }
+  }
+
+  #[no_mangle]
+  extern "C" fn main() {
+    DISPCNT.write(DisplayControl::new().with_video_mode(VideoMode::_0));
+    BG_PALETTE.index(0).write(Color::new());
+
+    crate::test_main();
+
+    BG_PALETTE.index(0).write(Color::from_rgb(5, 15, 25));
+    BG_PALETTE.index(1).write(Color::new());
+    BG0CNT
+      .write(BackgroundControl::new().with_charblock(0).with_screenblock(31));
+    DISPCNT.write(
+      DisplayControl::new().with_video_mode(VideoMode::_0).with_show_bg0(true),
+    );
+
+    // some niceties for people without mgba-test-runner
+    let tsb = TEXT_SCREENBLOCKS.get_frame(31).unwrap();
+    unsafe {
+      mem::set_u32x80_unchecked(
+        tsb.into_block::<1024>().as_mut_ptr().cast(),
+        0,
+        12,
+      );
+    }
+    Cga8x8Thick.bitunpack_4bpp(CHARBLOCK0_4BPP.as_region(), 0);
+
+    let row = tsb.get_row(9).unwrap().iter().skip(6);
+    for (addr, ch) in row.zip(b"all tests passed!") {
+      addr.write(TextEntry::new().with_tile(*ch as u16));
+    }
+
+    DISPSTAT.write(DisplayStatus::new());
+    bios::IntrWait(true, IrqBits::new());
+  }
+}
+
+#[cfg(test)]
+mod test {
+  use super::Align4;
+
+  #[test_case]
+  fn align4_as_u16_u32_slice() {
+    let a = Align4([0u8, 1u8, 2u8, 3u8]);
+    assert_eq!(a.as_u16_slice(), &[0x100_u16.to_le(), 0x302_u16.to_le()]);
+    assert_eq!(a.as_u32_slice(), &[0x3020100_u32.to_le()]);
+  }
+}
diff --git a/src/mem.rs b/src/mem.rs
index 0587234..7bfca54 100644
--- a/src/mem.rs
+++ b/src/mem.rs
@@ -1,3 +1,5 @@
+#![cfg_attr(not(feature = "on_gba"), allow(unused_variables))]
+
 use crate::macros::on_gba_or_unimplemented;
 
 /// Copies `u8` at a time between exclusive regions.