diff --git a/account/build.gradle b/account/build.gradle
index 9499119..ec043e7 100644
--- a/account/build.gradle
+++ b/account/build.gradle
@@ -31,7 +31,11 @@ buildscript {
 
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+
+    api 'io.reactivex.rxjava2:rxjava:2.1.9'
+
     testCompile 'junit:junit:4.12'
+    testImplementation 'org.amshove.kluent:kluent:1.34'
 }
 
 sourceCompatibility = '1.7'
diff --git a/account/src/main/java/io/github/novacrypto/account/AccountModel.kt b/account/src/main/java/io/github/novacrypto/account/AccountModel.kt
new file mode 100644
index 0000000..5fccd3c
--- /dev/null
+++ b/account/src/main/java/io/github/novacrypto/account/AccountModel.kt
@@ -0,0 +1,45 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto.account
+
+import io.reactivex.Observable
+import java.util.*
+
+data class AccountId(val uuid: UUID = UUID.randomUUID())
+
+data class AccountModel(
+        val id: AccountId = AccountId(),
+        val name: String = ""
+)
+
+fun <T : AccountModelIntent> Observable<T>.toAccountModelStream(): Observable<AccountModel> {
+    return this.scan(AccountModel(),
+            { model: AccountModel, intent: AccountModelIntent ->
+                accountModelReducer(intent, model)
+            })
+}
+
+fun accountModelReducer(intent: AccountModelIntent, model: AccountModel): AccountModel {
+    return when (intent) {
+        is AccountModelIntent.Rename -> model.copy(name = intent.name)
+    }
+}
diff --git a/account/src/main/java/io/github/novacrypto/account/AccountModelIntents.kt b/account/src/main/java/io/github/novacrypto/account/AccountModelIntents.kt
new file mode 100644
index 0000000..c6dfc88
--- /dev/null
+++ b/account/src/main/java/io/github/novacrypto/account/AccountModelIntents.kt
@@ -0,0 +1,44 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto.account
+
+sealed class AccountModelIntent {
+    class Rename(val name: String) : AccountModelIntent()
+}
+
+fun AccountModel.toAddIntent() =
+        UserModelIntent.AddAccountIntent(this).forward()
+
+fun AccountModel.toInsertIntent(index: Int) =
+        UserModelIntent.AddAccountIntent(this, index).forward()
+
+fun AccountModel.toRemoveIntent() =
+        UserModelIntent.RemoveAccountIntent(this.id).forward()
+
+fun AccountModel.toRenameIntent(newName: String) =
+        renameAccount(newName).toUserModelIntent(this).forward()
+
+fun renameAccount(newName: String) =
+        AccountModelIntent.Rename(newName)
+
+fun AccountModelIntent.toUserModelIntent(account: AccountModel) =
+        UserModelIntent.ForwardAccountModelIntent(account.id, this)
diff --git a/account/src/main/java/io/github/novacrypto/account/ErrorModel.kt b/account/src/main/java/io/github/novacrypto/account/ErrorModel.kt
new file mode 100644
index 0000000..576e823
--- /dev/null
+++ b/account/src/main/java/io/github/novacrypto/account/ErrorModel.kt
@@ -0,0 +1,28 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto.account
+
+data class ErrorModel(
+        val errorMessage: String
+)
+
+class UserReportableException(message: String) : Exception(message)
diff --git a/account/src/main/java/io/github/novacrypto/account/UserModel.kt b/account/src/main/java/io/github/novacrypto/account/UserModel.kt
new file mode 100644
index 0000000..b135bba
--- /dev/null
+++ b/account/src/main/java/io/github/novacrypto/account/UserModel.kt
@@ -0,0 +1,37 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto.account
+
+data class UserModel(
+        val accounts: List<AccountModel> = emptyList()
+)
+
+sealed class UserModelIntent {
+    class AddAccountIntent(val account: AccountModel, val index: Int? = null) : UserModelIntent()
+    class RemoveAccountIntent(val accountId: AccountId) : UserModelIntent()
+    class ForwardAccountModelIntent(
+            val accountId: AccountId,
+            val intent: AccountModelIntent
+    ) : UserModelIntent()
+}
+
+fun UserModelIntent.forward() = UserModelViewStateIntent.ForwardUserModelIntent(this)
diff --git a/account/src/main/java/io/github/novacrypto/account/UserModelViewState.kt b/account/src/main/java/io/github/novacrypto/account/UserModelViewState.kt
new file mode 100644
index 0000000..28ff510
--- /dev/null
+++ b/account/src/main/java/io/github/novacrypto/account/UserModelViewState.kt
@@ -0,0 +1,110 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto.account
+
+import io.reactivex.Observable
+
+data class UserModelViewState(
+        val userModel: UserModel = UserModel(),
+        val error: ErrorModel? = null,
+        val undoModel: UserModelViewStateUndoModel? = null
+)
+
+data class UserModelViewStateUndoModel(
+        val message: String,
+        val undoIntent: UserModelViewStateIntent
+)
+
+fun <T : UserModelViewStateIntent> Observable<T>.toUserModelStream(): Observable<UserModelViewState> {
+    return this.scan(UserModelViewState(),
+            { model: UserModelViewState, intent: UserModelViewStateIntent ->
+                model.transformWithIntent(intent)
+            })
+}
+
+private fun UserModelViewState.transformWithIntent(intent: UserModelViewStateIntent): UserModelViewState {
+    return when (intent) {
+        is UserModelViewStateIntent.DismissError -> copy(error = null)
+        is UserModelViewStateIntent.ForwardUserModelIntent ->
+            try {
+                val (newModel, undoModel) = userModel.transformWithIntent(intent.userModelIntent)
+                copy(userModel = newModel, undoModel = undoModel)
+            } catch (e: UserReportableException) {
+                copy(error = ErrorModel(e.message ?: ""))
+            }
+        is UserModelViewStateIntent.Undo ->
+            undoModel?.undoIntent?.let {
+                transformWithIntent(it
+                )
+            } ?: this
+    }
+}
+
+private fun UserModel.transformWithIntent(intent: UserModelIntent) =
+        when (intent) {
+            is UserModelIntent.AddAccountIntent -> {
+                copy(accounts = if (intent.index != null) {
+                    accounts.insert(intent.account, intent.index)
+                } else {
+                    accounts + intent.account
+                }).withNoUndo()
+            }
+            is UserModelIntent.RemoveAccountIntent -> {
+                withAccountAndIndexForId(intent.accountId) { account, index ->
+                    Pair(copy(accounts = accounts - account),
+                            UserModelViewStateUndoModel("Removed account '${account.name}'",
+                                    account.toInsertIntent(index)))
+                }
+            }
+            is UserModelIntent.ForwardAccountModelIntent -> {
+                withAccountAndIndexForId(intent.accountId) { account, index ->
+                    val newAccounts = accounts.replace(index, accountModelReducer(intent.intent, account))
+                    copy(accounts = newAccounts).withNoUndo()
+                }
+            }
+        }
+
+private fun <T> UserModel.withAccountAndIndexForId(accountId: AccountId, transform: (account: AccountModel, index: Int) -> T): T {
+    val accountIdx = accounts.indexOfFirst { it.id == accountId }.also {
+        if (it == -1) throw cannotFind(accountId)
+    }
+    val existingAccount = accounts[accountIdx]
+    return transform(existingAccount, accountIdx)
+}
+
+private fun UserModel.withNoUndo() = Pair(this, null)
+
+private inline fun <E> List<E>.copyAndModify(modify: MutableList<E>.() -> Unit): List<E> =
+        toMutableList().apply(modify)
+
+private fun <E> List<E>.insert(newItem: E, index: Int) =
+        copyAndModify {
+            this.add(index, newItem)
+        }
+
+private fun <E> List<E>.replace(index: Int, replacement: E) =
+        copyAndModify {
+            this[index] = replacement
+        }
+
+private fun cannotFind(accountId: AccountId) =
+        UserReportableException("Cannot find account $accountId")
diff --git a/account/src/main/java/io/github/novacrypto/account/UserModelViewStateIntents.kt b/account/src/main/java/io/github/novacrypto/account/UserModelViewStateIntents.kt
new file mode 100644
index 0000000..1586e98
--- /dev/null
+++ b/account/src/main/java/io/github/novacrypto/account/UserModelViewStateIntents.kt
@@ -0,0 +1,32 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto.account
+
+sealed class UserModelViewStateIntent {
+    class DismissError : UserModelViewStateIntent()
+    class Undo : UserModelViewStateIntent()
+    class ForwardUserModelIntent(
+            val userModelIntent: UserModelIntent
+    ) : UserModelViewStateIntent()
+}
+
+fun dismissError() = UserModelViewStateIntent.DismissError()
diff --git a/account/src/test/java/io/github/novacrypto/AccountModelTests.kt b/account/src/test/java/io/github/novacrypto/AccountModelTests.kt
new file mode 100644
index 0000000..ee0098e
--- /dev/null
+++ b/account/src/test/java/io/github/novacrypto/AccountModelTests.kt
@@ -0,0 +1,67 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto
+
+import io.github.novacrypto.account.AccountModel
+import io.github.novacrypto.account.renameAccount
+import io.github.novacrypto.account.toAccountModelStream
+import io.reactivex.Observable
+import org.amshove.kluent.`should be`
+import org.amshove.kluent.`should equal`
+import org.amshove.kluent.`should not equal`
+import org.junit.Test
+
+class AccountModelTests {
+
+    @Test
+    fun `new account gets new id`() {
+        AccountModel().id `should not equal` AccountModel().id
+    }
+
+}
+
+class AccountModelRenameIntentTests {
+
+    @Test
+    fun `user can rename account`() {
+        Observable.just(
+                renameAccount("My Account")
+        ).toAccountModelStream()
+                .assertWithLastElement {
+                    it.name `should equal` "My Account"
+                }
+    }
+
+    @Test
+    fun `user can rename account twice`() {
+        Observable.just(
+                renameAccount("My Account"),
+                renameAccount("My Account 2")
+        ).toAccountModelStream()
+                .assertWithLastElement {
+                    it.name `should equal` "My Account 2"
+                }
+                .assertWithLastTwoElements { penultimate, ultimate ->
+                    penultimate.id `should be` ultimate.id
+                }
+    }
+}
\ No newline at end of file
diff --git a/account/src/test/java/io/github/novacrypto/RxTestUtils.kt b/account/src/test/java/io/github/novacrypto/RxTestUtils.kt
new file mode 100644
index 0000000..ad6f0ea
--- /dev/null
+++ b/account/src/test/java/io/github/novacrypto/RxTestUtils.kt
@@ -0,0 +1,59 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto
+
+import io.reactivex.Observable
+import org.amshove.kluent.`should be`
+
+fun <T> Observable<T>.assertWithLastElement(function: (T) -> Unit): Observable<T> {
+    this.lastOrError()
+            .test()
+            .assertValue {
+                function(it)
+                true
+            }
+    return this
+}
+
+fun <T> Observable<T>.assertWithLastTwoElements(
+        function: (penultimate: T, ultimate: T) -> Unit
+) {
+    this.takeLast(2)
+            .test()
+            .values()
+            .also {
+                it.size `should be` 2
+                function(it[0], it[1])
+            }
+}
+
+fun <T> Observable<T>.assertWithLastAndThirdToLastElements(
+        function: (lastMinusTwo: T, last: T) -> Unit
+) {
+    this.takeLast(3)
+            .test()
+            .values()
+            .also {
+                it.size `should be` 3
+                function(it[0], it[2])
+            }
+}
diff --git a/account/src/test/java/io/github/novacrypto/UserModelIntentTests.kt b/account/src/test/java/io/github/novacrypto/UserModelIntentTests.kt
new file mode 100644
index 0000000..afcc137
--- /dev/null
+++ b/account/src/test/java/io/github/novacrypto/UserModelIntentTests.kt
@@ -0,0 +1,349 @@
+/*
+ *  NovaWallet, Cryptocurrency Wallet for Android
+ *  Copyright (C) 2018 Alan Evans, NovaCrypto
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *  Original source: https://github.com/NovaCrypto/NovaWallet
+ *  You can contact the authors via github issues.
+ */
+
+package io.github.novacrypto
+
+import io.github.novacrypto.account.*
+import io.reactivex.Observable
+import org.amshove.kluent.`should be`
+import org.amshove.kluent.`should equal`
+import org.amshove.kluent.`should not be`
+import org.junit.Test
+
+class UserModelIntentTests {
+
+    @Test
+    fun `initial user state`() {
+        Observable.empty<UserModelViewStateIntent>()
+                .toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts `should equal` emptyList()
+                }
+    }
+
+    @Test
+    fun `user can add an account`() {
+        val account = AccountModel()
+        Observable.just(account.toAddIntent())
+                .toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts `should equal` listOf(account)
+                }
+    }
+
+    @Test
+    fun `user can add two accounts`() {
+        val account1 = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(account1.toAddIntent(), account2.toAddIntent())
+                .toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts `should equal` listOf(account1, account2)
+                }
+    }
+}
+
+class UserModelRemoveAccountIntentTests {
+
+    @Test
+    fun `user can remove only account`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toAddIntent(),
+                account.toRemoveIntent()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts `should equal` emptyList()
+                }
+    }
+
+    @Test
+    fun `user can remove only account after rename`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toAddIntent(),
+                account.toRenameIntent("Account 1"),
+                account.toRemoveIntent()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts `should equal` emptyList()
+                }
+    }
+
+    @Test
+    fun `user can't remove account not added`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toRemoveIntent()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.error!!.errorMessage `should equal` "Cannot find account " + account.id
+                }
+    }
+
+    @Test
+    fun `user can remove first of two accounts`() {
+        val account1 = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(
+                account1.toAddIntent(),
+                account2.toAddIntent(),
+                account1.toRemoveIntent()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts `should equal` listOf(account2)
+                }
+    }
+
+    @Test
+    fun `user can remove second of two accounts`() {
+        val account1 = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(
+                account1.toAddIntent(),
+                account2.toAddIntent(),
+                account2.toRemoveIntent()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts `should equal` listOf(account1)
+                }
+    }
+}
+
+class AccountModelRenameUserIntentTests {
+
+    @Test
+    fun `user can rename account in user model`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toAddIntent(),
+                account.toRenameIntent("My Account")
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts.single().name `should equal` "My Account"
+                }
+    }
+
+    @Test
+    fun `user can rename twos account in the user model`() {
+        val account1 = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(
+                account1.toAddIntent(),
+                account2.toAddIntent(),
+                account1.toRenameIntent("My Account 1"),
+                account2.toRenameIntent("My Account 2")
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts.size `should equal` 2
+                    it.userModel.accounts[0].name `should equal` "My Account 1"
+                    it.userModel.accounts[1].name `should equal` "My Account 2"
+                }
+    }
+
+    @Test
+    fun `user can rename twos account in the user model in reverse order`() {
+        val account1 = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(
+                account1.toAddIntent(),
+                account2.toAddIntent(),
+                account2.toRenameIntent("My Account 2"),
+                account1.toRenameIntent("My Account 1")
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts.size `should equal` 2
+                    it.userModel.accounts[0].name `should equal` "My Account 1"
+                    it.userModel.accounts[1].name `should equal` "My Account 2"
+                }
+    }
+
+    @Test
+    fun `user can rename one account twice`() {
+        val account1 = AccountModel()
+        Observable.just(
+                account1.toAddIntent(),
+                account1.toRenameIntent("My Account A"),
+                account1.toRenameIntent("My Account B")
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts.single().name `should equal` "My Account B"
+                }
+    }
+
+    @Test
+    fun `user cant rename account not in list yet`() {
+        val account1 = AccountModel()
+        Observable.just(
+                account1.toRenameIntent("My Account A"),
+                account1.toAddIntent()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.userModel.accounts.single().name `should equal` ""
+                }
+    }
+
+    @Test
+    fun `rename of missing account results in error`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toRenameIntent("My Account A")
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.error!!.errorMessage `should equal` "Cannot find account " + account.id
+                }
+    }
+
+    @Test
+    fun `second error replaces first`() {
+        val account1 = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(
+                account1.toRenameIntent("My Account A"),
+                account2.toRenameIntent("My Account A")
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.error!!.errorMessage `should equal` "Cannot find account " + account2.id
+                }
+    }
+
+    @Test
+    fun `error is not automatically dismissed by another action`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toRenameIntent("My Account A"),
+                account.toAddIntent()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.error `should not be` null
+                }
+    }
+
+    @Test
+    fun `error should keep the previous state`() {
+        val account = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(
+                account.toAddIntent(),
+                account2.toRenameIntent("My Account A")
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.error `should not be` null
+                }
+                .assertWithLastTwoElements { penultimate, ultimate ->
+                    penultimate.userModel `should be` ultimate.userModel
+                }
+    }
+
+    @Test
+    fun `user can dismiss error`() {
+        val account = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(
+                account.toAddIntent(),
+                account2.toRenameIntent("My Account A"),
+                dismissError()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.error `should be` null
+                }
+                .assertWithLastAndThirdToLastElements { lastMinusTwo, last ->
+                    lastMinusTwo.userModel `should be` last.userModel
+                }
+    }
+
+}
+
+class UserModelUndo {
+
+    @Test
+    fun `user gets an undo message`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toAddIntent(),
+                account.toRenameIntent("My Account A"),
+                account.toRemoveIntent()
+        ).toUserModelStream()
+                .assertWithLastElement {
+                    it.undoModel!!.message `should equal` "Removed account 'My Account A'"
+                }
+    }
+
+    @Test
+    fun `user can undo a remove`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toAddIntent(),
+                account.toRenameIntent("My Account A"),
+                account.toRemoveIntent(),
+                undo()
+        ).toUserModelStream()
+                .assertWithLastAndThirdToLastElements { lastMinusTwo, last ->
+                    lastMinusTwo.userModel.accounts `should equal` last.userModel.accounts
+                }
+    }
+
+    @Test
+    fun `an undone remove is in the same position it was before (index 0)`() {
+        val account1 = AccountModel()
+        val account2 = AccountModel()
+        Observable.just(
+                account1.toAddIntent(),
+                account2.toAddIntent(),
+                account1.toRemoveIntent(),
+                undo()
+        ).toUserModelStream()
+                .assertWithLastAndThirdToLastElements { lastMinusTwo, last ->
+                    lastMinusTwo.userModel.accounts `should equal` last.userModel.accounts
+                }
+    }
+
+    @Test
+    fun `an undone remove is in the same position it was before (index 1)`() {
+        val account1 = AccountModel()
+        val account2 = AccountModel()
+        val account3 = AccountModel()
+        Observable.just(
+                account1.toAddIntent(),
+                account2.toAddIntent(),
+                account3.toAddIntent(),
+                account2.toRemoveIntent(),
+                undo()
+        ).toUserModelStream()
+                .assertWithLastAndThirdToLastElements { lastMinusTwo, last ->
+                    lastMinusTwo.userModel.accounts `should equal` last.userModel.accounts
+                }
+    }
+
+    @Test
+    fun `if there is nothing to undo, undo does nothing`() {
+        val account = AccountModel()
+        Observable.just(
+                account.toAddIntent(),
+                undo()
+        ).toUserModelStream()
+                .assertWithLastTwoElements { penultimate, ultimate ->
+                    penultimate `should be` ultimate
+                }
+    }
+}
+
+private fun undo(): UserModelViewStateIntent = UserModelViewStateIntent.Undo()
\ No newline at end of file