cmd/cue/cmd: add a Go test covering the exposed API

We have at least three users who got broken by a recent change of mine
to how the exposed cmd.New API behaves. Ahead of fixing that breakage,
add tests which mimic the reasonable uses of the public API
which I have seen from these users.

For #3458.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I80fa81c3f3d700fc575f3b337abae11ae55ea8de
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1202645
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

cmd/cue/cmd/root_test.go

@@ -0,0 +1,65 @@
+// Copyright 2024 The CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cmd_test
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"strings"
+	"testing"
+
+	"cuelang.org/go/cmd/cue/cmd"
+	"github.com/go-quicktest/qt"
+)
+
+// The cmd package exposes some APIs, which some users rely on.
+// Ensure that they continue to work as advertised.
+
+func TestCommand(t *testing.T) {
+	ctx := context.Background()
+
+	// Create one command and run it, only checking that it succeeds.
+	c, err := cmd.New([]string{"help", "export"})
+	c.SetOutput(io.Discard)
+	qt.Assert(t, qt.IsNil(err))
+	err = c.Run(ctx)
+	qt.Assert(t, qt.IsNil(err))
+
+	// Create another command and run it, expecting it to fail.
+	c, err = cmd.New([]string{"help", "nosuchcommand"})
+	c.SetOutput(io.Discard)
+	qt.Assert(t, qt.IsNil(err))
+	err = c.Run(ctx)
+	qt.Assert(t, qt.IsNotNil(err))
+
+	// Verify that SetInput and SetOutput work.
+	c, err = cmd.New([]string{"export", "-"})
+	c.SetInput(strings.NewReader("foo: 123\n"))
+	var buf bytes.Buffer
+	c.SetOutput(&buf)
+	qt.Assert(t, qt.IsNil(err))
+	err = c.Run(ctx)
+	qt.Assert(t, qt.IsNil(err))
+	qt.Assert(t, qt.Equals(buf.String(), "{\n    \"foo\": 123\n}\n"))
+
+	// Verify that we can use the API exposed by the embedded cobra command.
+	// TODO(mvdan): panics due to https://cuelang.org/issue/3458; fix it.
+	qt.Assert(t, qt.PanicMatches(func() {
+		c, err = cmd.New([]string{"fmt", "nosuchfile.cue"})
+		err = c.Execute()
+		qt.Assert(t, qt.IsNotNil(err))
+	}, "cmd/cue/cmd.mkRunE init ran twice"))
+}