test: cli test setup & test chain head

CLI actions lack unit tests. I decided to use the approach similar to
what I found in `send_test.go` using gomock, but I don't rely on custom
"service" implementations but mock the whole FullNode API.
This first commit validates the test setup by testing the simplest method
of the chain category, e.g. `chain head`.

This requires a minor refactor of the CLI action code:
- The constructor (`GetFullNodeAPI`) checks if there's an injected mock
API in the app Metadata and uses that in unit tests.
- Actions shouldn't use raw `fmt.*` but instead write to the `app.Writer`
so the CLI output is testable

cli/chain.go

@@ -67,6 +67,8 @@ var ChainHeadCmd = &cli.Command{
 	Name:  "head",
 	Usage: "Print chain head",
 	Action: func(cctx *cli.Context) error {
+		afmt := NewAppFmt(cctx.App)
+
 		api, closer, err := GetFullNodeAPI(cctx)
 		if err != nil {
 			return err
@@ -80,7 +82,7 @@ var ChainHeadCmd = &cli.Command{
 		}
 
 		for _, c := range head.Cids() {
-			fmt.Println(c)
+			afmt.Println(c)
 		}
 		return nil
 	},

cli/chain_test.go

@@ -0,0 +1,54 @@
+package cli
+
+import (
+	"bytes"
+	"context"
+	"regexp"
+	"testing"
+
+	"github.com/filecoin-project/lotus/api"
+	"github.com/filecoin-project/lotus/api/mocks"
+	"github.com/filecoin-project/lotus/chain/types/mock"
+	"github.com/golang/mock/gomock"
+	"github.com/stretchr/testify/assert"
+	ucli "github.com/urfave/cli/v2"
+)
+
+// newMockAppWithFullAPI returns a gomock-ed CLI app used for unit tests
+// see cli/util/api.go:GetFullNodeAPI for mock API injection
+func newMockAppWithFullAPI(t *testing.T, cmd *ucli.Command) (*ucli.App, *mocks.MockFullNode, *bytes.Buffer, func()) {
+	app := ucli.NewApp()
+	app.Commands = ucli.Commands{cmd}
+	app.Setup()
+
+	// create and inject the mock API into app Metadata
+	ctrl := gomock.NewController(t)
+	mockFullNode := mocks.NewMockFullNode(ctrl)
+	var fullNode api.FullNode = mockFullNode
+	app.Metadata["test-full-api"] = fullNode
+
+	// this will only work if the implementation uses the app.Writer,
+	// if it uses fmt.*, it has to be refactored
+	buf := &bytes.Buffer{}
+	app.Writer = buf
+
+	return app, mockFullNode, buf, ctrl.Finish
+}
+
+func TestChainHead(t *testing.T) {
+	app, mockApi, buf, done := newMockAppWithFullAPI(t, WithCategory("chain", ChainHeadCmd))
+	defer done()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	ts := mock.TipSet(mock.MkBlock(nil, 0, 0))
+	gomock.InOrder(
+		mockApi.EXPECT().ChainHead(ctx).Return(ts, nil),
+	)
+
+	err := app.Run([]string{"chain", "head"})
+	assert.NoError(t, err)
+
+	assert.Regexp(t, regexp.MustCompile(ts.Cids()[0].String()), buf.String())
+}

cli/util/api.go

@@ -223,6 +223,11 @@ func GetCommonAPI(ctx *cli.Context) (api.CommonNet, jsonrpc.ClientCloser, error)
 }
 
 func GetFullNodeAPI(ctx *cli.Context) (v0api.FullNode, jsonrpc.ClientCloser, error) {
+	// use the mocked API in CLI unit tests, see cli/chain_test.go for mock definition
+	if mock, ok := ctx.App.Metadata["test-full-api"]; ok {
+		return &v0api.WrapperV1Full{FullNode: mock.(v1api.FullNode)}, func() {}, nil
+	}
+
 	if tn, ok := ctx.App.Metadata["testnode-full"]; ok {
 		return &v0api.WrapperV1Full{FullNode: tn.(v1api.FullNode)}, func() {}, nil
 	}