refactor: allow the mock module to be used multiple times as base ibc…

… application in middleware stack (cosmos#892)

## Description

Currently the `AppModule` assumes a single scoped keeper. This doesn't allow the mock module to be used as a base application for different middleware stack (ica stack, fee stack, etc)

I broke the API because I think it is cleaner. If we want this to be non API breaking, I can try to readjust

ref: cosmos#891 

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

- [ ] Targeted PR against correct branch (see [CONTRIBUTING.md](https://github.com/cosmos/ibc-go/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
- [ ] Code follows the [module structure standards](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules/structure.md).
- [ ] Wrote unit and integration [tests](https://github.com/cosmos/ibc-go/blob/master/CONTRIBUTING.md#testing)
- [ ] Updated relevant documentation (`docs/`) or specification (`x/<module>/spec/`)
- [ ] Added relevant `godoc` [comments](https://blog.golang.org/godoc-documenting-go-code).
- [ ] Added a relevant changelog entry to the `Unreleased` section in `CHANGELOG.md`
- [ ] Re-reviewed `Files changed` in the Github PR explorer
- [ ] Review `Codecov Report` in the comment section below once CI passes

CHANGELOG.md

@@ -53,6 +53,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * (modules/core/02-client) [\#536](https://github.com/cosmos/ibc-go/pull/536) `GetSelfConsensusState` return type changed from bool to error.
 * (channel) [\#644](https://github.com/cosmos/ibc-go/pull/644) Removes `CounterpartyHops` function from the ChannelKeeper.
 * (testing) [\#776](https://github.com/cosmos/ibc-go/pull/776) Adding helper fn to generate capability name for testing callbacks 
+* (testing) [\#892](https://github.com/cosmos/ibc-go/pull/892) IBC Mock modules store the scoped keeper and portID within the IBCMockApp. They also maintain reference to the AppModule to update the AppModule's list of IBC applications it references. Allows for the mock module to be reused as a base application in middleware stacks.
 * (channel) [\#882](https://github.com/cosmos/ibc-go/pull/882) The `WriteAcknowledgement` API now takes `exported.Acknowledgement` instead of a byte array
 
 ### State Machine Breaking

testing/README.md

@@ -296,6 +296,7 @@ The mock module may also be leveraged to act as a base application in the instan
 
 The mock IBC module contains a `MockIBCApp`. This struct contains a function field for every IBC App Module callback. 
 Each of these functions can be individually set to mock expected behaviour of a base application. 
+The portID and scoped keeper for the `MockIBCApp` should be set within `MockIBCApp` before calling `NewIBCModule`.
 
 For example, if one wanted to test that the base application cannot affect the outcome of the `OnChanOpenTry` callback, the mock module base application callback could be updated as such:
 ```go

testing/mock/ibc_app.go

@@ -2,6 +2,7 @@ package mock
 
 import (
 	sdk "github.com/cosmos/cosmos-sdk/types"
+	capabilitykeeper "github.com/cosmos/cosmos-sdk/x/capability/keeper"
 	capabilitytypes "github.com/cosmos/cosmos-sdk/x/capability/types"
 
 	channeltypes "github.com/cosmos/ibc-go/v3/modules/core/04-channel/types"
@@ -10,6 +11,9 @@ import (
 
 // MockIBCApp contains IBC application module callbacks as defined in 05-port.
 type MockIBCApp struct {
+	PortID       string
+	ScopedKeeper capabilitykeeper.ScopedKeeper
+
 	OnChanOpenInit func(
 		ctx sdk.Context,
 		order channeltypes.Order,
@@ -81,3 +85,11 @@ type MockIBCApp struct {
 		relayer sdk.AccAddress,
 	) error
 }
+
+// NewMockIBCApp returns a MockIBCApp. An empty PortID indicates the mock app doesn't bind/claim ports.
+func NewMockIBCApp(portID string, scopedKeeper capabilitykeeper.ScopedKeeper) *MockIBCApp {
+	return &MockIBCApp{
+		PortID:       portID,
+		ScopedKeeper: scopedKeeper,
+	}
+}

testing/mock/ibc_module.go

@@ -6,7 +6,6 @@ import (
 	"strconv"
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
-	capabilitykeeper "github.com/cosmos/cosmos-sdk/x/capability/keeper"
 	capabilitytypes "github.com/cosmos/cosmos-sdk/x/capability/types"
 
 	channeltypes "github.com/cosmos/ibc-go/v3/modules/core/04-channel/types"
@@ -16,15 +15,16 @@ import (
 
 // IBCModule implements the ICS26 callbacks for testing/mock.
 type IBCModule struct {
-	IBCApp       *MockIBCApp // base application of an IBC middleware stack
-	scopedKeeper capabilitykeeper.ScopedKeeper
+	appModule *AppModule
+	IBCApp    *MockIBCApp // base application of an IBC middleware stack
 }
 
 // NewIBCModule creates a new IBCModule given the underlying mock IBC application and scopedKeeper.
-func NewIBCModule(app *MockIBCApp, scopedKeeper capabilitykeeper.ScopedKeeper) IBCModule {
+func NewIBCModule(appModule *AppModule, app *MockIBCApp) IBCModule {
+	appModule.ibcApps = append(appModule.ibcApps, app)
 	return IBCModule{
-		IBCApp:       app,
-		scopedKeeper: scopedKeeper,
+		appModule: appModule,
+		IBCApp:    app,
 	}
 }
 
@@ -39,7 +39,7 @@ func (im IBCModule) OnChanOpenInit(
 	}
 
 	// Claim channel capability passed back by IBC module
-	if err := im.scopedKeeper.ClaimCapability(ctx, chanCap, host.ChannelCapabilityPath(portID, channelID)); err != nil {
+	if err := im.IBCApp.ScopedKeeper.ClaimCapability(ctx, chanCap, host.ChannelCapabilityPath(portID, channelID)); err != nil {
 		return err
 	}
 
@@ -56,7 +56,7 @@ func (im IBCModule) OnChanOpenTry(
 	}
 
 	// Claim channel capability passed back by IBC module
-	if err := im.scopedKeeper.ClaimCapability(ctx, chanCap, host.ChannelCapabilityPath(portID, channelID)); err != nil {
+	if err := im.IBCApp.ScopedKeeper.ClaimCapability(ctx, chanCap, host.ChannelCapabilityPath(portID, channelID)); err != nil {
 		return "", err
 	}
 
@@ -107,7 +107,7 @@ func (im IBCModule) OnRecvPacket(ctx sdk.Context, packet channeltypes.Packet, re
 
 	// set state by claiming capability to check if revert happens return
 	capName := GetMockRecvCanaryCapabilityName(packet)
-	if _, err := im.scopedKeeper.NewCapability(ctx, capName); err != nil {
+	if _, err := im.IBCApp.ScopedKeeper.NewCapability(ctx, capName); err != nil {
 		// application callback called twice on same packet sequence
 		// must never occur
 		panic(err)
@@ -129,7 +129,7 @@ func (im IBCModule) OnAcknowledgementPacket(ctx sdk.Context, packet channeltypes
 	}
 
 	capName := GetMockAckCanaryCapabilityName(packet)
-	if _, err := im.scopedKeeper.NewCapability(ctx, capName); err != nil {
+	if _, err := im.IBCApp.ScopedKeeper.NewCapability(ctx, capName); err != nil {
 		// application callback called twice on same packet sequence
 		// must never occur
 		panic(err)
@@ -145,7 +145,7 @@ func (im IBCModule) OnTimeoutPacket(ctx sdk.Context, packet channeltypes.Packet,
 	}
 
 	capName := GetMockTimeoutCanaryCapabilityName(packet)
-	if _, err := im.scopedKeeper.NewCapability(ctx, capName); err != nil {
+	if _, err := im.IBCApp.ScopedKeeper.NewCapability(ctx, capName); err != nil {
 		// application callback called twice on same packet sequence
 		// must never occur
 		panic(err)

testing/mock/mock.go

@@ -8,7 +8,6 @@ import (
 	codectypes "github.com/cosmos/cosmos-sdk/codec/types"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/cosmos/cosmos-sdk/types/module"
-	capabilitykeeper "github.com/cosmos/cosmos-sdk/x/capability/keeper"
 	capabilitytypes "github.com/cosmos/cosmos-sdk/x/capability/types"
 	"github.com/gorilla/mux"
 	"github.com/grpc-ecosystem/grpc-gateway/runtime"
@@ -89,15 +88,14 @@ func (AppModuleBasic) GetQueryCmd() *cobra.Command {
 // AppModule represents the AppModule for the mock module.
 type AppModule struct {
 	AppModuleBasic
-	scopedKeeper capabilitykeeper.ScopedKeeper
-	portKeeper   PortKeeper
+	ibcApps    []*MockIBCApp
+	portKeeper PortKeeper
 }
 
 // NewAppModule returns a mock AppModule instance.
-func NewAppModule(sk capabilitykeeper.ScopedKeeper, pk PortKeeper) AppModule {
+func NewAppModule(pk PortKeeper) AppModule {
 	return AppModule{
-		scopedKeeper: sk,
-		portKeeper:   pk,
+		portKeeper: pk,
 	}
 }
 
@@ -124,9 +122,13 @@ func (am AppModule) RegisterServices(module.Configurator) {}
 
 // InitGenesis implements the AppModule interface.
 func (am AppModule) InitGenesis(ctx sdk.Context, cdc codec.JSONCodec, data json.RawMessage) []abci.ValidatorUpdate {
-	// bind mock port ID
-	cap := am.portKeeper.BindPort(ctx, ModuleName)
-	am.scopedKeeper.ClaimCapability(ctx, cap, host.PortPath(ModuleName))
+	for _, ibcApp := range am.ibcApps {
+		if ibcApp.PortID != "" {
+			// bind mock portID
+			cap := am.portKeeper.BindPort(ctx, ibcApp.PortID)
+			ibcApp.ScopedKeeper.ClaimCapability(ctx, cap, host.PortPath(ModuleName))
+		}
+	}
 
 	return []abci.ValidatorUpdate{}
 }

testing/simapp/app.go

@@ -350,8 +350,8 @@ func NewSimApp(
 
 	// NOTE: the IBC mock keeper and application module is used only for testing core IBC. Do
 	// not replicate if you do not need to test core IBC or light clients.
-	mockModule := ibcmock.NewAppModule(scopedIBCMockKeeper, &app.IBCKeeper.PortKeeper)
-	mockIBCModule := ibcmock.NewIBCModule(&ibcmock.MockIBCApp{}, scopedIBCMockKeeper)
+	mockModule := ibcmock.NewAppModule(&app.IBCKeeper.PortKeeper)
+	mockIBCModule := ibcmock.NewIBCModule(&mockModule, ibcmock.NewMockIBCApp(ibcmock.ModuleName, scopedIBCMockKeeper))
 
 	app.ICAControllerKeeper = icacontrollerkeeper.NewKeeper(
 		appCodec, keys[icacontrollertypes.StoreKey], app.GetSubspace(icacontrollertypes.SubModuleName),
@@ -369,7 +369,7 @@ func NewSimApp(
 	icaModule := ica.NewAppModule(&app.ICAControllerKeeper, &app.ICAHostKeeper)
 
 	// initialize ICA module with mock module as the authentication module on the controller side
-	icaAuthModule := ibcmock.NewIBCModule(&ibcmock.MockIBCApp{}, scopedICAMockKeeper)
+	icaAuthModule := ibcmock.NewIBCModule(&mockModule, ibcmock.NewMockIBCApp("", scopedICAMockKeeper))
 	app.ICAAuthModule = icaAuthModule
 
 	icaControllerIBCModule := icacontroller.NewIBCModule(app.ICAControllerKeeper, icaAuthModule)