diff --git a/src/block_group.rs b/src/block_group.rs
index 739fa32..14974e1 100644
--- a/src/block_group.rs
+++ b/src/block_group.rs
@@ -1,3 +1,15 @@
+#[cfg(test)]
+use std::mem;
+#[cfg(test)]
+use std::slice;
+
+#[cfg(not(test))]
+use core::mem;
+#[cfg(not(test))]
+use core::slice;
+
+use error::Error;
+
 /// The Block Group Descriptor Table contains a descriptor for each block group
 /// within the file system. The number of block groups within the file system,
 /// and correspondingly, the number of entries in the Block Group Descriptor
@@ -27,3 +39,44 @@ pub struct BlockGroupDescriptor {
     #[doc(hidden)]
     _reserved: [u8; 14],
 }
+
+impl BlockGroupDescriptor {
+    pub fn find_descriptor_table<'a>(
+        haystack: &'a mut [u8],
+        offset: isize,
+        count: usize,
+    ) -> Result<&'a mut [BlockGroupDescriptor], Error> {
+        let offset = (2048 + offset) as usize;
+        let end = offset + count * mem::size_of::<BlockGroupDescriptor>();
+        if haystack.len() < end {
+            return Err(Error::OutOfBounds(end));
+        }
+
+        let ptr = unsafe {
+            haystack.as_mut_ptr().offset(offset as isize)
+                as *mut BlockGroupDescriptor
+        };
+        let slice = unsafe { slice::from_raw_parts_mut(ptr, count) };
+        Ok(slice)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn find() {
+        let mut buffer = vec![0_u8; 4096];
+        let addr = &buffer[2048] as *const _ as usize;
+        // magic
+        let table =
+            BlockGroupDescriptor::find_descriptor_table(&mut buffer, 0, 0);
+        assert!(
+            table.is_ok(),
+            "Err({:?})",
+            table.err().unwrap_or_else(|| unreachable!()),
+        );
+        assert_eq!(table.unwrap().as_ptr() as usize, addr);
+    }
+}
diff --git a/src/superblock.rs b/src/superblock.rs
index 62ca518..bb59bfd 100644
--- a/src/superblock.rs
+++ b/src/superblock.rs
@@ -1,15 +1,10 @@
 #[cfg(test)]
 use std::mem;
-#[cfg(test)]
-use std::slice;
 
 #[cfg(not(test))]
 use core::mem;
-#[cfg(not(test))]
-use core::slice;
 
 use error::Error;
-use block_group::BlockGroupDescriptor;
 
 /// Ext2 signature (0xef53), used to help confirm the presence of Ext2 on a
 /// volume
@@ -175,29 +170,6 @@ impl Superblock {
         }
     }
 
-    pub fn find_block_table<'a>(
-        &self,
-        haystack: &'a mut [u8],
-        offset: isize,
-    ) -> Result<&'a mut [BlockGroupDescriptor], Error> {
-        let count = self.block_group_count()
-            .map_err(|(a, b)| Error::BadBlockGroupCount(a, b))?
-            as usize;
-
-        let offset = (2048 + offset) as usize;
-        let end = offset + count * mem::size_of::<BlockGroupDescriptor>();
-        if haystack.len() < end {
-            return Err(Error::OutOfBounds(end));
-        }
-
-        let ptr = unsafe {
-            haystack.as_mut_ptr().offset(offset as isize)
-                as *mut BlockGroupDescriptor
-        };
-        let slice = unsafe { slice::from_raw_parts_mut(ptr, count) };
-        Ok(slice)
-    }
-
     #[inline]
     pub fn block_size(&self) -> usize {
         1024 << self.log_block_size