make uninit_mask a unit test

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -2,6 +2,8 @@
 
 mod init_mask;
 mod provenance_map;
+#[cfg(test)]
+mod tests;
 
 use std::borrow::Cow;
 use std::fmt;

compiler/rustc_middle/src/mir/interpret/allocation/init_mask.rs

@@ -150,7 +150,7 @@ impl InitMask {
     }
 
     #[inline]
-    fn get(&self, i: Size) -> bool {
+    pub fn get(&self, i: Size) -> bool {
         let (block, bit) = Self::bit_index(i);
         (self.blocks[block] & (1 << bit)) != 0
     }

compiler/rustc_middle/src/mir/interpret/allocation/tests.rs

@@ -0,0 +1,19 @@
+use super::*;
+
+#[test]
+fn uninit_mask() {
+    let mut mask = InitMask::new(Size::from_bytes(500), false);
+    assert!(!mask.get(Size::from_bytes(499)));
+    mask.set_range(alloc_range(Size::from_bytes(499), Size::from_bytes(1)), true);
+    assert!(mask.get(Size::from_bytes(499)));
+    mask.set_range((100..256).into(), true);
+    for i in 0..100 {
+        assert!(!mask.get(Size::from_bytes(i)), "{i} should not be set");
+    }
+    for i in 100..256 {
+        assert!(mask.get(Size::from_bytes(i)), "{i} should be set");
+    }
+    for i in 256..499 {
+        assert!(!mask.get(Size::from_bytes(i)), "{i} should not be set");
+    }
+}