diff --git a/Makefile b/Makefile
index fa26b47..c7a604c 100644
--- a/Makefile
+++ b/Makefile
@@ -82,6 +82,7 @@ target/debug/libpolytreewm.a:
 
 test: $(TEST_EXE)
 	@echo "$(TEST_EXE)" | awk '{ OFS="\n"; $$1=$$1 } 1' | /bin/sh
+	$(CARGO) test
 
 clean:
 	rm -f $(ALL_OBJ) $(ALL_EXE)
diff --git a/src/lib.rs b/src/lib.rs
index 9dc5ba6..eba48aa 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,11 +1,24 @@
 use std::os::raw::*;
 
-const MIN_BORDER_WIDTH: c_int = 0;
 const MAX_BORDER_WIDTH: c_int = 10000;
 
 #[no_mangle]
 pub extern "C" fn constraints_border_width(border_width: c_int) -> c_int {
-	if border_width < MIN_BORDER_WIDTH { return MIN_BORDER_WIDTH }
 	if border_width > MAX_BORDER_WIDTH { return MAX_BORDER_WIDTH }
 	border_width
 }
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn test_constraints_border_width() {
+		assert_eq!(constraints_border_width(0), 0);
+		assert_eq!(constraints_border_width(10), 10);
+		assert_eq!(constraints_border_width(10_000), 10_000);
+
+		assert_eq!(constraints_border_width(10_001), 10_000);
+		assert_eq!(constraints_border_width(20_000), 10_000);
+	}
+}