diff --git a/src/termdict/mod.rs b/src/termdict/mod.rs
index e77783300..7ac74fbeb 100644
--- a/src/termdict/mod.rs
+++ b/src/termdict/mod.rs
@@ -1,7 +1,29 @@
+/*!
+The term dictionary main role is to associate the sorted [`Term`s](../struct.Term.html) to
+a [`TermInfo`](../postings/struct.TermInfo.html) struct that contains some meta-information
+about the term.
+
+Internally, the term dictionary relies on the `fst` crate to store
+a sorted mapping that associate each term to its rank in the lexicographical order.
+For instance, in a dictionary containing the sorted terms "abba", "bjork", "blur" and "donovan",
+the `TermOrdinal` are respectively `0`, `1`, `2`, and `3`.
+
+For `u64`-terms, tantivy explicitely uses a `BigEndian` representation to ensure that the
+lexicographical order matches the natural order of integers.
+
+`i64`-terms are transformed to `u64` using a continuous mapping `val ⟶ val - i64::min_value()`
+and then treated as a `u64`.
+
+`f64`-terms are transformed to `u64` using a mapping that preserve order, and are then treated
+as `u64`.
+
+A second datastructure makes it possible to access a [`TermInfo`](../postings/struct.TermInfo.html).
+*/
+
 use tantivy_fst::automaton::AlwaysMatch;
 
 mod fst_termdict;
-// mod traits;
+use fst_termdict as termdict;
 
 #[cfg(test)]
 mod tests;
@@ -11,12 +33,12 @@ pub type TermOrdinal = u64;
 
 /// The term dictionary contains all of the terms in
 /// `tantivy index` in a sorted manner.
-pub type TermDictionary = self::fst_termdict::TermDictionary;
+pub type TermDictionary = self::termdict::TermDictionary;
 
 /// Builder for the new term dictionary.
 ///
 /// Inserting must be done in the order of the `keys`.
-pub type TermDictionaryBuilder<W> = self::fst_termdict::TermDictionaryBuilder<W>;
+pub type TermDictionaryBuilder<W> = self::termdict::TermDictionaryBuilder<W>;
 
 /// Given a list of sorted term streams,
 /// returns an iterator over sorted unique terms.
@@ -25,8 +47,8 @@ pub type TermDictionaryBuilder<W> = self::fst_termdict::TermDictionaryBuilder<W>
 /// - the term
 /// - a slice with the ordinal of the segments containing
 /// the terms.
-pub type TermMerger<'a> = self::fst_termdict::TermMerger<'a>;
+pub type TermMerger<'a> = self::termdict::TermMerger<'a>;
 
 /// `TermStreamer` acts as a cursor over a range of terms of a segment.
 /// Terms are guaranteed to be sorted.
-pub type TermStreamer<'a, A = AlwaysMatch> = self::fst_termdict::TermStreamer<'a, A>;
+pub type TermStreamer<'a, A = AlwaysMatch> = self::termdict::TermStreamer<'a, A>;
diff --git a/src/termdict/tests.rs b/src/termdict/tests.rs
index 1a58e43b6..c7d3afc7f 100644
--- a/src/termdict/tests.rs
+++ b/src/termdict/tests.rs
@@ -1,421 +1,420 @@
+use super::{TermDictionary, TermDictionaryBuilder, TermStreamer};
+use crate::core::Index;
+use crate::directory::{Directory, FileSlice, RAMDirectory};
+use crate::postings::TermInfo;
+use crate::schema::{Schema, TEXT};
+use std::path::PathBuf;
+use std::str;
 
-    use super::{TermDictionary, TermDictionaryBuilder, TermStreamer};
-    use crate::core::Index;
-    use crate::directory::{Directory, FileSlice, RAMDirectory};
-    use crate::postings::TermInfo;
-    use crate::schema::{Schema, TEXT};
-    use std::path::PathBuf;
-    use std::str;
+const BLOCK_SIZE: usize = 1_500;
 
-    const BLOCK_SIZE: usize = 1_500;
-
-    fn make_term_info(term_ord: u64) -> TermInfo {
-        let offset = |term_ord: u64| term_ord * 100 + term_ord * term_ord;
-        TermInfo {
-            doc_freq: term_ord as u32,
-            postings_start_offset: offset(term_ord),
-            postings_stop_offset: offset(term_ord + 1),
-            positions_idx: offset(term_ord) * 2u64,
-        }
+fn make_term_info(term_ord: u64) -> TermInfo {
+    let offset = |term_ord: u64| term_ord * 100 + term_ord * term_ord;
+    TermInfo {
+        doc_freq: term_ord as u32,
+        postings_start_offset: offset(term_ord),
+        postings_stop_offset: offset(term_ord + 1),
+        positions_idx: offset(term_ord) * 2u64,
     }
+}
 
-    #[test]
-    fn test_empty_term_dictionary() {
-        let empty = TermDictionary::empty();
-        assert!(empty.stream().next().is_none());
+#[test]
+fn test_empty_term_dictionary() {
+    let empty = TermDictionary::empty();
+    assert!(empty.stream().next().is_none());
+}
+
+#[test]
+fn test_term_ordinals() -> crate::Result<()> {
+    const COUNTRIES: [&'static str; 7] = [
+        "San Marino",
+        "Serbia",
+        "Slovakia",
+        "Slovenia",
+        "Spain",
+        "Sweden",
+        "Switzerland",
+    ];
+    let directory = RAMDirectory::create();
+    let path = PathBuf::from("TermDictionary");
+    {
+        let write = directory.open_write(&path)?;
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
+        for term in COUNTRIES.iter() {
+            term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
+        }
+        term_dictionary_builder.finish()?;
     }
-
-    #[test]
-    fn test_term_ordinals() -> crate::Result<()> {
-        const COUNTRIES: [&'static str; 7] = [
-            "San Marino",
-            "Serbia",
-            "Slovakia",
-            "Slovenia",
-            "Spain",
-            "Sweden",
-            "Switzerland",
-        ];
-        let directory = RAMDirectory::create();
-        let path = PathBuf::from("TermDictionary");
-        {
-            let write = directory.open_write(&path)?;
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
-            for term in COUNTRIES.iter() {
-                term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
-            }
-            term_dictionary_builder.finish()?;
-        }
-        let term_file = directory.open_read(&path)?;
-        let term_dict: TermDictionary = TermDictionary::open(term_file)?;
-        for (term_ord, term) in COUNTRIES.iter().enumerate() {
-            assert_eq!(term_dict.term_ord(term).unwrap(), term_ord as u64);
-            let mut bytes = vec![];
-            assert!(term_dict.ord_to_term(term_ord as u64, &mut bytes));
-            assert_eq!(bytes, term.as_bytes());
-        }
-        Ok(())
+    let term_file = directory.open_read(&path)?;
+    let term_dict: TermDictionary = TermDictionary::open(term_file)?;
+    for (term_ord, term) in COUNTRIES.iter().enumerate() {
+        assert_eq!(term_dict.term_ord(term).unwrap(), term_ord as u64);
+        let mut bytes = vec![];
+        assert!(term_dict.ord_to_term(term_ord as u64, &mut bytes));
+        assert_eq!(bytes, term.as_bytes());
     }
+    Ok(())
+}
 
-    #[test]
-    fn test_term_dictionary_simple() -> crate::Result<()> {
-        let directory = RAMDirectory::create();
-        let path = PathBuf::from("TermDictionary");
-        {
-            let write = directory.open_write(&path)?;
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
-            term_dictionary_builder.insert("abc".as_bytes(), &make_term_info(34u64))?;
-            term_dictionary_builder.insert("abcd".as_bytes(), &make_term_info(346u64))?;
-            term_dictionary_builder.finish()?;
-        }
-        let file = directory.open_read(&path)?;
-        let term_dict: TermDictionary = TermDictionary::open(file)?;
-        assert_eq!(term_dict.get("abc").unwrap().doc_freq, 34u32);
-        assert_eq!(term_dict.get("abcd").unwrap().doc_freq, 346u32);
-        let mut stream = term_dict.stream();
-        {
-            {
-                let (k, v) = stream.next().unwrap();
-                assert_eq!(k.as_ref(), "abc".as_bytes());
-                assert_eq!(v.doc_freq, 34u32);
-            }
-            assert_eq!(stream.key(), "abc".as_bytes());
-            assert_eq!(stream.value().doc_freq, 34u32);
-        }
-        {
-            {
-                let (k, v) = stream.next().unwrap();
-                assert_eq!(k, "abcd".as_bytes());
-                assert_eq!(v.doc_freq, 346u32);
-            }
-            assert_eq!(stream.key(), "abcd".as_bytes());
-            assert_eq!(stream.value().doc_freq, 346u32);
-        }
-        assert!(!stream.advance());
-        Ok(())
+#[test]
+fn test_term_dictionary_simple() -> crate::Result<()> {
+    let directory = RAMDirectory::create();
+    let path = PathBuf::from("TermDictionary");
+    {
+        let write = directory.open_write(&path)?;
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
+        term_dictionary_builder.insert("abc".as_bytes(), &make_term_info(34u64))?;
+        term_dictionary_builder.insert("abcd".as_bytes(), &make_term_info(346u64))?;
+        term_dictionary_builder.finish()?;
     }
-
-    #[test]
-    fn test_term_iterator() -> crate::Result<()> {
-        let mut schema_builder = Schema::builder();
-        let text_field = schema_builder.add_text_field("text", TEXT);
-        let index = Index::create_in_ram(schema_builder.build());
+    let file = directory.open_read(&path)?;
+    let term_dict: TermDictionary = TermDictionary::open(file)?;
+    assert_eq!(term_dict.get("abc").unwrap().doc_freq, 34u32);
+    assert_eq!(term_dict.get("abcd").unwrap().doc_freq, 346u32);
+    let mut stream = term_dict.stream();
+    {
         {
-            let mut index_writer = index.writer_for_tests()?;
-            index_writer.add_document(doc!(text_field=>"a b d f"));
-            index_writer.commit()?;
-            index_writer.add_document(doc!(text_field=>"a b c d f"));
-            index_writer.commit()?;
-            index_writer.add_document(doc!(text_field => "e f"));
-            index_writer.commit()?;
+            let (k, v) = stream.next().unwrap();
+            assert_eq!(k.as_ref(), "abc".as_bytes());
+            assert_eq!(v.doc_freq, 34u32);
         }
-        let searcher = index.reader()?.searcher();
-
-        let field_searcher = searcher.field(text_field)?;
-        let mut term_it = field_searcher.terms();
-        let mut term_string = String::new();
-        while term_it.advance() {
-            //let term = Term::from_bytes(term_it.key());
-            term_string.push_str(str::from_utf8(term_it.key()).expect("test"));
-        }
-        assert_eq!(&*term_string, "abcdef");
-        Ok(())
+        assert_eq!(stream.key(), "abc".as_bytes());
+        assert_eq!(stream.value().doc_freq, 34u32);
     }
-
-    #[test]
-    fn test_term_dictionary_stream() -> crate::Result<()> {
-        let ids: Vec<_> = (0u32..10_000u32)
-            .map(|i| (format!("doc{:0>6}", i), i))
-            .collect();
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
-            for &(ref id, ref i) in &ids {
-                term_dictionary_builder
-                    .insert(id.as_bytes(), &make_term_info(*i as u64))
-                    .unwrap();
-            }
-            term_dictionary_builder.finish().unwrap()
-        };
-        let term_file = FileSlice::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::open(term_file)?;
+    {
         {
-            let mut streamer = term_dictionary.stream();
-            let mut i = 0;
-            while let Some((streamer_k, streamer_v)) = streamer.next() {
-                let &(ref key, ref v) = &ids[i];
-                assert_eq!(streamer_k.as_ref(), key.as_bytes());
-                assert_eq!(streamer_v, &make_term_info(*v as u64));
-                i += 1;
-            }
+            let (k, v) = stream.next().unwrap();
+            assert_eq!(k, "abcd".as_bytes());
+            assert_eq!(v.doc_freq, 346u32);
         }
-
-        let &(ref key, ref val) = &ids[2047];
-        assert_eq!(
-            term_dictionary.get(key.as_bytes()),
-            Some(make_term_info(*val as u64))
-        );
-        Ok(())
+        assert_eq!(stream.key(), "abcd".as_bytes());
+        assert_eq!(stream.value().doc_freq, 346u32);
     }
+    assert!(!stream.advance());
+    Ok(())
+}
 
-    #[test]
-    fn test_stream_high_range_prefix_suffix() -> crate::Result<()> {
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
-            // term requires more than 16bits
-            term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxy", &make_term_info(1))?;
-            term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxyz", &make_term_info(2))?;
-            term_dictionary_builder.insert("abr", &make_term_info(3))?;
-            term_dictionary_builder.finish()?
-        };
-        let term_dict_file = FileSlice::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::open(term_dict_file)?;
-        let mut kv_stream = term_dictionary.stream();
-        assert!(kv_stream.advance());
-        assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxy".as_bytes());
-        assert_eq!(kv_stream.value(), &make_term_info(1));
-        assert!(kv_stream.advance());
-        assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxyz".as_bytes());
-        assert_eq!(kv_stream.value(), &make_term_info(2));
-        assert!(kv_stream.advance());
-        assert_eq!(kv_stream.key(), "abr".as_bytes());
-        assert_eq!(kv_stream.value(), &make_term_info(3));
-        assert!(!kv_stream.advance());
-        Ok(())
+#[test]
+fn test_term_iterator() -> crate::Result<()> {
+    let mut schema_builder = Schema::builder();
+    let text_field = schema_builder.add_text_field("text", TEXT);
+    let index = Index::create_in_ram(schema_builder.build());
+    {
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(text_field=>"a b d f"));
+        index_writer.commit()?;
+        index_writer.add_document(doc!(text_field=>"a b c d f"));
+        index_writer.commit()?;
+        index_writer.add_document(doc!(text_field => "e f"));
+        index_writer.commit()?;
     }
+    let searcher = index.reader()?.searcher();
 
-    #[test]
-    fn test_stream_range() -> crate::Result<()> {
-        let ids: Vec<_> = (0u32..10_000u32)
-            .map(|i| (format!("doc{:0>6}", i), i))
-            .collect();
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
-            for &(ref id, ref i) in &ids {
-                term_dictionary_builder
-                    .insert(id.as_bytes(), &make_term_info(*i as u64))
-                    .unwrap();
-            }
-            term_dictionary_builder.finish().unwrap()
-        };
-
-        let file = FileSlice::from(buffer);
-
-        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
-        {
-            for i in (0..20).chain(6000..8_000) {
-                let &(ref target_key, _) = &ids[i];
-                let mut streamer = term_dictionary
-                    .range()
-                    .ge(target_key.as_bytes())
-                    .into_stream();
-                for j in 0..3 {
-                    let (streamer_k, streamer_v) = streamer.next().unwrap();
-                    let &(ref key, ref v) = &ids[i + j];
-                    assert_eq!(str::from_utf8(streamer_k.as_ref()).unwrap(), key);
-                    assert_eq!(streamer_v.doc_freq, *v);
-                    assert_eq!(streamer_v, &make_term_info(*v as u64));
-                }
-            }
-        }
-
-        {
-            for i in (0..20).chain(BLOCK_SIZE - 10..BLOCK_SIZE + 10) {
-                let &(ref target_key, _) = &ids[i];
-                let mut streamer = term_dictionary
-                    .range()
-                    .gt(target_key.as_bytes())
-                    .into_stream();
-                for j in 0..3 {
-                    let (streamer_k, streamer_v) = streamer.next().unwrap();
-                    let &(ref key, ref v) = &ids[i + j + 1];
-                    assert_eq!(streamer_k.as_ref(), key.as_bytes());
-                    assert_eq!(streamer_v.doc_freq, *v);
-                }
-            }
-        }
-
-        {
-            for i in (0..20).chain(BLOCK_SIZE - 10..BLOCK_SIZE + 10) {
-                for j in 0..3 {
-                    let &(ref fst_key, _) = &ids[i];
-                    let &(ref last_key, _) = &ids[i + j];
-                    let mut streamer = term_dictionary
-                        .range()
-                        .ge(fst_key.as_bytes())
-                        .lt(last_key.as_bytes())
-                        .into_stream();
-                    for _ in 0..j {
-                        assert!(streamer.next().is_some());
-                    }
-                    assert!(streamer.next().is_none());
-                }
-            }
-        }
-        Ok(())
+    let field_searcher = searcher.field(text_field)?;
+    let mut term_it = field_searcher.terms();
+    let mut term_string = String::new();
+    while term_it.advance() {
+        //let term = Term::from_bytes(term_it.key());
+        term_string.push_str(str::from_utf8(term_it.key()).expect("test"));
     }
+    assert_eq!(&*term_string, "abcdef");
+    Ok(())
+}
 
-    #[test]
-    fn test_empty_string() -> crate::Result<()> {
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+#[test]
+fn test_term_dictionary_stream() -> crate::Result<()> {
+    let ids: Vec<_> = (0u32..10_000u32)
+        .map(|i| (format!("doc{:0>6}", i), i))
+        .collect();
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+        for &(ref id, ref i) in &ids {
             term_dictionary_builder
-                .insert(&[], &make_term_info(1 as u64))
+                .insert(id.as_bytes(), &make_term_info(*i as u64))
                 .unwrap();
-            term_dictionary_builder
-                .insert(&[1u8], &make_term_info(2 as u64))
-                .unwrap();
-            term_dictionary_builder.finish().unwrap()
-        };
-        let file = FileSlice::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
-        let mut stream = term_dictionary.stream();
-        assert!(stream.advance());
-        assert!(stream.key().is_empty());
-        assert!(stream.advance());
-        assert_eq!(stream.key(), &[1u8]);
-        assert!(!stream.advance());
-        Ok(())
+        }
+        term_dictionary_builder.finish().unwrap()
+    };
+    let term_file = FileSlice::from(buffer);
+    let term_dictionary: TermDictionary = TermDictionary::open(term_file)?;
+    {
+        let mut streamer = term_dictionary.stream();
+        let mut i = 0;
+        while let Some((streamer_k, streamer_v)) = streamer.next() {
+            let &(ref key, ref v) = &ids[i];
+            assert_eq!(streamer_k.as_ref(), key.as_bytes());
+            assert_eq!(streamer_v, &make_term_info(*v as u64));
+            i += 1;
+        }
     }
 
-    #[test]
-    fn test_stream_range_boundaries() -> crate::Result<()> {
-        let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(Vec::new())?;
-            for i in 0u8..10u8 {
-                let number_arr = [i; 1];
-                term_dictionary_builder.insert(&number_arr, &make_term_info(i as u64))?;
-            }
-            term_dictionary_builder.finish()?
-        };
-        let file = FileSlice::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
+    let &(ref key, ref val) = &ids[2047];
+    assert_eq!(
+        term_dictionary.get(key.as_bytes()),
+        Some(make_term_info(*val as u64))
+    );
+    Ok(())
+}
 
-        let value_list = |mut streamer: TermStreamer<'_>, backwards: bool| {
-            let mut res: Vec<u32> = vec![];
-            while let Some((_, ref v)) = streamer.next() {
-                res.push(v.doc_freq);
-            }
-            if backwards {
-                res.reverse();
-            }
-            res
-        };
-        {
-            let range = term_dictionary.range().backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
+#[test]
+fn test_stream_high_range_prefix_suffix() -> crate::Result<()> {
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+        // term requires more than 16bits
+        term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxy", &make_term_info(1))?;
+        term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxyz", &make_term_info(2))?;
+        term_dictionary_builder.insert("abr", &make_term_info(3))?;
+        term_dictionary_builder.finish()?
+    };
+    let term_dict_file = FileSlice::from(buffer);
+    let term_dictionary: TermDictionary = TermDictionary::open(term_dict_file)?;
+    let mut kv_stream = term_dictionary.stream();
+    assert!(kv_stream.advance());
+    assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxy".as_bytes());
+    assert_eq!(kv_stream.value(), &make_term_info(1));
+    assert!(kv_stream.advance());
+    assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxyz".as_bytes());
+    assert_eq!(kv_stream.value(), &make_term_info(2));
+    assert!(kv_stream.advance());
+    assert_eq!(kv_stream.key(), "abr".as_bytes());
+    assert_eq!(kv_stream.value(), &make_term_info(3));
+    assert!(!kv_stream.advance());
+    Ok(())
+}
+
+#[test]
+fn test_stream_range() -> crate::Result<()> {
+    let ids: Vec<_> = (0u32..10_000u32)
+        .map(|i| (format!("doc{:0>6}", i), i))
+        .collect();
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+        for &(ref id, ref i) in &ids {
+            term_dictionary_builder
+                .insert(id.as_bytes(), &make_term_info(*i as u64))
+                .unwrap();
         }
-        {
-            let range = term_dictionary.range().ge([2u8]).into_stream();
-            assert_eq!(
-                value_list(range, false),
-                vec![2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().ge([2u8]).backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().gt([2u8]).into_stream();
-            assert_eq!(
-                value_list(range, false),
-                vec![3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().gt([2u8]).backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().lt([6u8]).into_stream();
-            assert_eq!(
-                value_list(range, false),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().lt([6u8]).backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().le([6u8]).into_stream();
-            assert_eq!(
-                value_list(range, false),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().le([6u8]).backward().into_stream();
-            assert_eq!(
-                value_list(range, true),
-                vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32]
-            );
-        }
-        {
-            let range = term_dictionary.range().ge([0u8]).lt([5u8]).into_stream();
-            assert_eq!(value_list(range, false), vec![0u32, 1u32, 2u32, 3u32, 4u32]);
-        }
-        {
-            let range = term_dictionary
+        term_dictionary_builder.finish().unwrap()
+    };
+
+    let file = FileSlice::from(buffer);
+
+    let term_dictionary: TermDictionary = TermDictionary::open(file)?;
+    {
+        for i in (0..20).chain(6000..8_000) {
+            let &(ref target_key, _) = &ids[i];
+            let mut streamer = term_dictionary
                 .range()
-                .ge([0u8])
-                .lt([5u8])
-                .backward()
+                .ge(target_key.as_bytes())
                 .into_stream();
-            assert_eq!(value_list(range, true), vec![0u32, 1u32, 2u32, 3u32, 4u32]);
-        }
-        Ok(())
-    }
-
-    #[test]
-    fn test_automaton_search() -> crate::Result<()> {
-        use crate::query::DFAWrapper;
-        use levenshtein_automata::LevenshteinAutomatonBuilder;
-
-        const COUNTRIES: [&'static str; 7] = [
-            "San Marino",
-            "Serbia",
-            "Slovakia",
-            "Slovenia",
-            "Spain",
-            "Sweden",
-            "Switzerland",
-        ];
-
-        let directory = RAMDirectory::create();
-        let path = PathBuf::from("TermDictionary");
-        {
-            let write = directory.open_write(&path)?;
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
-            for term in COUNTRIES.iter() {
-                term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
+            for j in 0..3 {
+                let (streamer_k, streamer_v) = streamer.next().unwrap();
+                let &(ref key, ref v) = &ids[i + j];
+                assert_eq!(str::from_utf8(streamer_k.as_ref()).unwrap(), key);
+                assert_eq!(streamer_v.doc_freq, *v);
+                assert_eq!(streamer_v, &make_term_info(*v as u64));
             }
-            term_dictionary_builder.finish()?;
         }
-        let file = directory.open_read(&path)?;
-        let term_dict: TermDictionary = TermDictionary::open(file)?;
-
-        // We can now build an entire dfa.
-        let lev_automaton_builder = LevenshteinAutomatonBuilder::new(2, true);
-        let automaton = DFAWrapper(lev_automaton_builder.build_dfa("Spaen"));
-
-        let mut range = term_dict.search(automaton).into_stream();
-
-        // get the first finding
-        assert!(range.advance());
-        assert_eq!("Spain".as_bytes(), range.key());
-        assert!(!range.advance());
-        Ok(())
     }
+
+    {
+        for i in (0..20).chain(BLOCK_SIZE - 10..BLOCK_SIZE + 10) {
+            let &(ref target_key, _) = &ids[i];
+            let mut streamer = term_dictionary
+                .range()
+                .gt(target_key.as_bytes())
+                .into_stream();
+            for j in 0..3 {
+                let (streamer_k, streamer_v) = streamer.next().unwrap();
+                let &(ref key, ref v) = &ids[i + j + 1];
+                assert_eq!(streamer_k.as_ref(), key.as_bytes());
+                assert_eq!(streamer_v.doc_freq, *v);
+            }
+        }
+    }
+
+    {
+        for i in (0..20).chain(BLOCK_SIZE - 10..BLOCK_SIZE + 10) {
+            for j in 0..3 {
+                let &(ref fst_key, _) = &ids[i];
+                let &(ref last_key, _) = &ids[i + j];
+                let mut streamer = term_dictionary
+                    .range()
+                    .ge(fst_key.as_bytes())
+                    .lt(last_key.as_bytes())
+                    .into_stream();
+                for _ in 0..j {
+                    assert!(streamer.next().is_some());
+                }
+                assert!(streamer.next().is_none());
+            }
+        }
+    }
+    Ok(())
+}
+
+#[test]
+fn test_empty_string() -> crate::Result<()> {
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+        term_dictionary_builder
+            .insert(&[], &make_term_info(1 as u64))
+            .unwrap();
+        term_dictionary_builder
+            .insert(&[1u8], &make_term_info(2 as u64))
+            .unwrap();
+        term_dictionary_builder.finish().unwrap()
+    };
+    let file = FileSlice::from(buffer);
+    let term_dictionary: TermDictionary = TermDictionary::open(file)?;
+    let mut stream = term_dictionary.stream();
+    assert!(stream.advance());
+    assert!(stream.key().is_empty());
+    assert!(stream.advance());
+    assert_eq!(stream.key(), &[1u8]);
+    assert!(!stream.advance());
+    Ok(())
+}
+
+#[test]
+fn test_stream_range_boundaries() -> crate::Result<()> {
+    let buffer: Vec<u8> = {
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(Vec::new())?;
+        for i in 0u8..10u8 {
+            let number_arr = [i; 1];
+            term_dictionary_builder.insert(&number_arr, &make_term_info(i as u64))?;
+        }
+        term_dictionary_builder.finish()?
+    };
+    let file = FileSlice::from(buffer);
+    let term_dictionary: TermDictionary = TermDictionary::open(file)?;
+
+    let value_list = |mut streamer: TermStreamer<'_>, backwards: bool| {
+        let mut res: Vec<u32> = vec![];
+        while let Some((_, ref v)) = streamer.next() {
+            res.push(v.doc_freq);
+        }
+        if backwards {
+            res.reverse();
+        }
+        res
+    };
+    {
+        let range = term_dictionary.range().backward().into_stream();
+        assert_eq!(
+            value_list(range, true),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().ge([2u8]).into_stream();
+        assert_eq!(
+            value_list(range, false),
+            vec![2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().ge([2u8]).backward().into_stream();
+        assert_eq!(
+            value_list(range, true),
+            vec![2u32, 3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().gt([2u8]).into_stream();
+        assert_eq!(
+            value_list(range, false),
+            vec![3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().gt([2u8]).backward().into_stream();
+        assert_eq!(
+            value_list(range, true),
+            vec![3u32, 4u32, 5u32, 6u32, 7u32, 8u32, 9u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().lt([6u8]).into_stream();
+        assert_eq!(
+            value_list(range, false),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().lt([6u8]).backward().into_stream();
+        assert_eq!(
+            value_list(range, true),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().le([6u8]).into_stream();
+        assert_eq!(
+            value_list(range, false),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().le([6u8]).backward().into_stream();
+        assert_eq!(
+            value_list(range, true),
+            vec![0u32, 1u32, 2u32, 3u32, 4u32, 5u32, 6u32]
+        );
+    }
+    {
+        let range = term_dictionary.range().ge([0u8]).lt([5u8]).into_stream();
+        assert_eq!(value_list(range, false), vec![0u32, 1u32, 2u32, 3u32, 4u32]);
+    }
+    {
+        let range = term_dictionary
+            .range()
+            .ge([0u8])
+            .lt([5u8])
+            .backward()
+            .into_stream();
+        assert_eq!(value_list(range, true), vec![0u32, 1u32, 2u32, 3u32, 4u32]);
+    }
+    Ok(())
+}
+
+#[test]
+fn test_automaton_search() -> crate::Result<()> {
+    use crate::query::DFAWrapper;
+    use levenshtein_automata::LevenshteinAutomatonBuilder;
+
+    const COUNTRIES: [&'static str; 7] = [
+        "San Marino",
+        "Serbia",
+        "Slovakia",
+        "Slovenia",
+        "Spain",
+        "Sweden",
+        "Switzerland",
+    ];
+
+    let directory = RAMDirectory::create();
+    let path = PathBuf::from("TermDictionary");
+    {
+        let write = directory.open_write(&path)?;
+        let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
+        for term in COUNTRIES.iter() {
+            term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
+        }
+        term_dictionary_builder.finish()?;
+    }
+    let file = directory.open_read(&path)?;
+    let term_dict: TermDictionary = TermDictionary::open(file)?;
+
+    // We can now build an entire dfa.
+    let lev_automaton_builder = LevenshteinAutomatonBuilder::new(2, true);
+    let automaton = DFAWrapper(lev_automaton_builder.build_dfa("Spaen"));
+
+    let mut range = term_dict.search(automaton).into_stream();
+
+    // get the first finding
+    assert!(range.advance());
+    assert_eq!("Spain".as_bytes(), range.key());
+    assert!(!range.advance());
+    Ok(())
+}