diff --git a/src/bin/flat/tube/metric.rs b/src/bin/flat/tube/metric.rs
index b64603b..8bd5724 100644
--- a/src/bin/flat/tube/metric.rs
+++ b/src/bin/flat/tube/metric.rs
@@ -49,29 +49,36 @@ impl Metric for Tube {
 	}
 }
 
-#[test]
-fn test_tube_metric_derivs() {
-	struct Approx(Tube);
-	impl Metric for Approx {
-		fn sqrt_at(&self, pos: Vec2) -> Decomp2 { self.0.sqrt_at(pos) }
-	}
-	let testee = Tube {
-		inner_radius: 30.0,
-		outer_radius: 50.0,
-		internal_halflength: 100.0,
-		external_halflength: 300.0,
-	};
-	let approx = Approx(testee);
-	let epsilon = 1.0e-3;
-	let margin = 1.0 / 16.0;
-	let mul = 1.0 + margin;
-	for x in itertools_num::linspace(-mul * testee.outer_radius, mul * testee.outer_radius, 100) {
-		for y in itertools_num::linspace(-mul * testee.external_halflength, mul * testee.external_halflength, 100) {
-			let pos = vec2(x, y);
-			let computed = testee.part_derivs_at(pos);
-			let reference = approx.part_derivs_at(pos);
-			let eq = (0..2).all(|coord| computed[coord].abs_diff_eq(reference[coord], epsilon));
-			assert!(eq, "Bad derivative computation at {pos}:\n  explicit:  {computed:?}\n  numerical: {reference:?}\n");
+#[cfg(test)]
+mod test {
+	use glam::{Vec2, vec2};
+	use crate::riemann::{Decomp2, Metric};
+	use super::Tube;
+
+	#[test]
+	fn test_tube_metric_derivs() {
+		struct Approx(Tube);
+		impl Metric for Approx {
+			fn sqrt_at(&self, pos: Vec2) -> Decomp2 { self.0.sqrt_at(pos) }
+		}
+		let testee = Tube {
+			inner_radius: 30.0,
+			outer_radius: 50.0,
+			internal_halflength: 100.0,
+			external_halflength: 300.0,
+		};
+		let approx = Approx(testee);
+		let epsilon = 1.0e-3;
+		let margin = 1.0 / 16.0;
+		let mul = 1.0 + margin;
+		for x in itertools_num::linspace(-mul * testee.outer_radius, mul * testee.outer_radius, 100) {
+			for y in itertools_num::linspace(-mul * testee.external_halflength, mul * testee.external_halflength, 100) {
+				let pos = vec2(x, y);
+				let computed = testee.part_derivs_at(pos);
+				let reference = approx.part_derivs_at(pos);
+				let eq = (0..2).all(|coord| computed[coord].abs_diff_eq(reference[coord], epsilon));
+				assert!(eq, "Bad derivative computation at {pos}:\n  explicit:  {computed:?}\n  numerical: {reference:?}\n");
+			}
 		}
 	}
 }