diff --git a/README.md b/README.md
index 8ab7093..174eedb 100644
--- a/README.md
+++ b/README.md
@@ -4,8 +4,14 @@ An in-process, in-memory database for Go.
 
 ## TO DO
 
-* MDB Tests
-  * map index
-  * btree index
-  * btree iterator
+* mapindex_test.go
+  * TestFullMapIndex
+  * TestPartialMapIndex
+* btreeindex_test.go
+  * TestFullBTreeIndex
+  * TestPartialBTreeIndex
+* btreeiterator_test.go
+* collection
+* database
   * WAL shipping
+  * WAL shipping with network disconnects
diff --git a/mapindex_test.go b/mapindex_test.go
index f1bd643..0d25d63 100644
--- a/mapindex_test.go
+++ b/mapindex_test.go
@@ -1,6 +1,7 @@
 package mdb
 
 import (
+	"errors"
 	"fmt"
 	"reflect"
 	"testing"
@@ -170,12 +171,193 @@ func TestFullMapIndex(t *testing.T) {
 		return users
 	})
 
-	// update index field change key error
+	run("update change key error", func(t *testing.T, db *DB) map[string]*User {
+		users := map[string]*User{}
 
-	// update error from func
-	// update w/ ErrAbortUpdate
-	// update not found.
-	// update conflict.
+		for i := uint64(1); i < 10; i++ {
+			user := &User{
+				ID:    db.Users.c.NextID(),
+				Email: fmt.Sprintf("a.%d@c.com", i),
+				Name:  fmt.Sprintf("name.%d", i),
+				ExtID: fmt.Sprintf("EXTID.%d", i),
+			}
+			if _, err := db.Users.c.Insert(*user); err != nil {
+				t.Fatal(err)
+			}
+			users[user.Email] = user
+		}
+
+		var email string
+		for key := range users {
+			email = key
+			break
+		}
+
+		err := db.Users.emailMap.Update(email, func(u User) (User, error) {
+			u.Email = "test@x.com"
+			return u, nil
+		})
+		if err != ErrMismatchedIDs {
+			t.Fatal(err)
+		}
+
+		return users
+	})
+
+	run("update function error", func(t *testing.T, db *DB) map[string]*User {
+		users := map[string]*User{}
+
+		for i := uint64(1); i < 10; i++ {
+			user := &User{
+				ID:    db.Users.c.NextID(),
+				Email: fmt.Sprintf("a.%d@c.com", i),
+				Name:  fmt.Sprintf("name.%d", i),
+				ExtID: fmt.Sprintf("EXTID.%d", i),
+			}
+			if _, err := db.Users.c.Insert(*user); err != nil {
+				t.Fatal(err)
+			}
+			users[user.Email] = user
+		}
+
+		var email string
+		for key := range users {
+			email = key
+			break
+		}
+
+		myErr := errors.New("hello")
+
+		err := db.Users.emailMap.Update(email, func(u User) (User, error) {
+			return u, myErr
+		})
+		if err != myErr {
+			t.Fatal(err)
+		}
+
+		return users
+	})
+
+	run("update ErrAbortUpdate", func(t *testing.T, db *DB) map[string]*User {
+		users := map[string]*User{}
+
+		for i := uint64(1); i < 10; i++ {
+			user := &User{
+				ID:    db.Users.c.NextID(),
+				Email: fmt.Sprintf("a.%d@c.com", i),
+				Name:  fmt.Sprintf("name.%d", i),
+				ExtID: fmt.Sprintf("EXTID.%d", i),
+			}
+			if _, err := db.Users.c.Insert(*user); err != nil {
+				t.Fatal(err)
+			}
+			users[user.Email] = user
+		}
+
+		var email string
+		for key := range users {
+			email = key
+			break
+		}
+
+		err := db.Users.emailMap.Update(email, func(u User) (User, error) {
+			return u, ErrAbortUpdate
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		return users
+	})
+
+	run("update ErrNotFound", func(t *testing.T, db *DB) map[string]*User {
+		users := map[string]*User{}
+
+		for i := uint64(1); i < 10; i++ {
+			user := &User{
+				ID:    db.Users.c.NextID(),
+				Email: fmt.Sprintf("a.%d@c.com", i),
+				Name:  fmt.Sprintf("name.%d", i),
+				ExtID: fmt.Sprintf("EXTID.%d", i),
+			}
+			if _, err := db.Users.c.Insert(*user); err != nil {
+				t.Fatal(err)
+			}
+			users[user.Email] = user
+		}
+
+		var email string
+		for key := range users {
+			email = key
+			break
+		}
+
+		err := db.Users.emailMap.Update(email+"x", func(u User) (User, error) {
+			return u, nil
+		})
+		if err != ErrNotFound {
+			t.Fatal(err)
+		}
+
+		return users
+	})
+
+	run("insert conflict", func(t *testing.T, db *DB) map[string]*User {
+		users := map[string]*User{}
+
+		user := &User{
+			ID:    db.Users.c.NextID(),
+			Email: "a@b.com",
+			Name:  "a",
+			ExtID: "",
+		}
+
+		if _, err := db.Users.c.Insert(*user); err != nil {
+			t.Fatal(err)
+		}
+		users[user.Email] = user
+
+		user2 := User{
+			ID:    db.Users.c.NextID(),
+			Email: "a@b.com",
+			Name:  "someone else",
+			ExtID: "123",
+		}
+
+		_, err := db.Users.c.Insert(user2)
+		if !errors.Is(err, ErrDuplicate) {
+			t.Fatal(err)
+		}
+
+		return users
+	})
+
+	run("update conflict", func(t *testing.T, db *DB) map[string]*User {
+		users := map[string]*User{}
+
+		user1 := &User{ID: db.Users.c.NextID(), Email: "a@b.com", Name: "a"}
+		user2 := &User{ID: db.Users.c.NextID(), Email: "x@y.com", Name: "x"}
+
+		users[user1.Email] = user1
+		users[user2.Email] = user2
+
+		for _, u := range users {
+			if _, err := db.Users.c.Insert(*u); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		err := db.Users.c.Update(user2.ID, func(u User) (User, error) {
+			u.Email = "a@b.com"
+			return u, nil
+		})
+		if !errors.Is(err, ErrDuplicate) {
+			t.Fatal(err)
+		}
+
+		return users
+	})
+	// update conflict
 }
 
 func TestPartialMapIndex(t *testing.T) {
@@ -184,12 +366,11 @@ func TestPartialMapIndex(t *testing.T) {
 	// insert outside index
 	// insert and delete in index
 	// insert and delete outside index
-	// insert withing index
-	// update out of index
+	// update outside index
 	// update into index
-	// update error from func
+	// update function error
 	// udpate ErrAbortUpdate
-	// update not found
+	// update ErrNotFound
 	// update conflict in to in
 	// update conflict out to in
 }