diff --git a/btreeindex_test.go b/btreeindex_test.go
index 8ad7da7..0de492c 100644
--- a/btreeindex_test.go
+++ b/btreeindex_test.go
@@ -43,8 +43,6 @@ func TestFullBTreeIndex(t *testing.T) {
 		return users
 	})
 
-	// Update
-
 	run("update", func(t *testing.T, db *DB) (users []*User) {
 		users = append(users,
 			&User{ID: db.Users.c.NextID(), Email: "a@b.com", Name: "aaa"},
@@ -120,14 +118,117 @@ func TestFullBTreeIndex(t *testing.T) {
 }
 
 func TestPartialBTreeIndex(t *testing.T) {
-	// empty
-	// insert into
-	// insert outside
-	// upate out to in
-	// update out to out
-	// update in to in
-	// update in to out
-	// delete outside
-	// delete in
-	// load w/duplicate
+
+	// Test against the name index.
+	run := func(name string, inner func(t *testing.T, db *DB) []*User) {
+		testWithDB(t, name, func(t *testing.T, db *DB) {
+			expected := inner(t, db)
+
+			if err := db.Users.nameBTree.EqualsList(expected); err != nil {
+				t.Fatal(err)
+			}
+
+			db.Close()
+			db = OpenDB(db.root, true)
+
+			if err := db.Users.nameBTree.EqualsList(expected); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+
+	run("empty", func(t *testing.T, db *DB) []*User {
+		return []*User{}
+	})
+
+	run("insert", func(t *testing.T, db *DB) (users []*User) {
+		users = append(users,
+			&User{ID: db.Users.c.NextID(), Email: "a@b.com", Name: "xxx"},
+			&User{ID: db.Users.c.NextID(), Email: "c@d.com", Name: "ggg"},
+			&User{ID: db.Users.c.NextID(), Email: "e@f.com", Name: "aaa"})
+
+		for _, u := range users {
+			if _, err := db.Users.c.Insert(*u); err != nil {
+				t.Fatal(err)
+			}
+		}
+		users[0], users[2] = users[2], users[0]
+
+		return users
+	})
+
+	run("insert duplicates", func(t *testing.T, db *DB) (users []*User) {
+		users = append(users,
+			&User{ID: db.Users.c.NextID(), Email: "a@b.com", Name: "xxx"},
+			&User{ID: db.Users.c.NextID(), Email: "c@d.com", Name: "ggg"},
+			&User{ID: db.Users.c.NextID(), Email: "e@f.com", Name: "xxx"})
+
+		for _, u := range users {
+			if _, err := db.Users.c.Insert(*u); err != nil {
+				t.Fatal(err)
+			}
+		}
+		users = []*User{users[1], users[0], users[2]}
+		return users
+	})
+
+	run("update", func(t *testing.T, db *DB) (users []*User) {
+		users = append(users,
+			&User{ID: db.Users.c.NextID(), Email: "a@b.com", Name: "ccc"},
+			&User{ID: db.Users.c.NextID(), Email: "c@d.com", Name: "aaa"},
+			&User{ID: db.Users.c.NextID(), Email: "e@f.com", Name: "bbb"})
+
+		for _, u := range users {
+			if _, err := db.Users.c.Insert(*u); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		err := db.Users.c.Update(users[1].ID, func(u User) (User, error) {
+			u.Name = "ccc"
+			return u, nil
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+		users[1].Name = "ccc"
+
+		users = []*User{users[2], users[0], users[1]}
+		return users
+	})
+
+	run("update", func(t *testing.T, db *DB) (users []*User) {
+		users = append(users,
+			&User{ID: db.Users.c.NextID(), Email: "a@b.com", Name: "bbb"},
+			&User{ID: db.Users.c.NextID(), Email: "c@d.com", Name: "aaa"},
+			&User{ID: db.Users.c.NextID(), Email: "e@f.com", Name: "bbb"})
+
+		for _, u := range users {
+			if _, err := db.Users.c.Insert(*u); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		db.Users.c.Delete(users[1].ID)
+		users = []*User{users[0], users[2]}
+		return users
+	})
+}
+
+func TestBTreeIndex_load_ErrDuplicate(t *testing.T) {
+	testWithDB(t, "", func(t *testing.T, db *DB) {
+		idx := NewBTreeIndex(
+			db.Users.c,
+			func(lhs, rhs *User) bool { return lhs.ExtID < rhs.ExtID },
+			nil)
+
+		users := map[uint64]*User{
+			1: {ID: 1, Email: "x@y.com", Name: "xx", ExtID: "x"},
+			2: {ID: 2, Email: "a@b.com", Name: "aa", ExtID: "x"},
+		}
+
+		if err := idx.load(users); err != ErrDuplicate {
+			t.Fatal(err)
+		}
+	})
 }
diff --git a/btreeiterator_test.go b/btreeiterator_test.go
new file mode 100644
index 0000000..6f3612e
--- /dev/null
+++ b/btreeiterator_test.go
@@ -0,0 +1,42 @@
+package mdb
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestBTreeIterator(t *testing.T) {
+	testWithDB(t, "min/max matches iterator", func(t *testing.T, db *DB) {
+		users := []User{
+			{ID: db.Users.c.NextID(), Email: "a@b.com", Name: "aaa"},
+			{ID: db.Users.c.NextID(), Email: "e@f.com", Name: "bbb"},
+			{ID: db.Users.c.NextID(), Email: "c@d.com", Name: "ccc"},
+		}
+		for _, u := range users {
+			if _, err := db.Users.c.Insert(u); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		it := db.Users.nameBTree.Ascend()
+		if !it.Next() {
+			t.Fatal("No next")
+		}
+		u := it.Value()
+		if !reflect.DeepEqual(u, users[0]) {
+			t.Fatal(u, users[0])
+		}
+		it.Close()
+
+		it = db.Users.nameBTree.Descend()
+		if !it.Next() {
+			t.Fatal("No next")
+		}
+		u = it.Value()
+		if !reflect.DeepEqual(u, users[2]) {
+			t.Fatal(u, users[2])
+		}
+		it.Close()
+
+	})
+}