cuepls: first integration test

Basic integration test to ensure that everything is plumbed together.

Notice how this integration test actually opens a Go file. We haven't at
this stage made changes to cuepls (formerly gopls) to know about CUE
files. That follows in a later CL. This integration test confirms that
we have a working end-to-end setup. Which then allows for more
aggressive tidy up to take place.

For now we do not run the integration test on Windows because it doesn't
work. That is covered by https://cuelang.org/issue/2752.

For #142

Signed-off-by: Paul Jolly <paul@myitcv.io>
Change-Id: I036c4a344dd1b1d339cf744db029c60789e547cb
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1174172
TryBot-Result: CUEcueckoo <cueckoo@gmail.com>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

cmd/cuepls/internal/test/integration/base/base_test.go

@@ -0,0 +1,33 @@
+//go:build !windows
+
+package feature
+
+import (
+	"testing"
+
+	"cuelang.org/go/internal/golangorgx/gopls/hooks"
+	. "cuelang.org/go/internal/golangorgx/gopls/test/integration"
+	"github.com/go-quicktest/qt"
+)
+
+func TestMain(m *testing.M) {
+	Main(m, hooks.Options)
+}
+
+func TestFormatFile(t *testing.T) {
+	const files = `
+-- go.mod --
+module mod.com
+
+go 1.12
+-- foo.go --
+	package foo
+`
+	Run(t, files, func(t *testing.T, env *Env) {
+		env.OpenFile("foo.go")
+		env.FormatBuffer("foo.go")
+		got := env.BufferText("foo.go")
+		want := "package foo\n"
+		qt.Assert(t, qt.Equals(got, want))
+	})
+}