Add the readme of the goa plugin

plugin/goa/README.md

@@ -0,0 +1,46 @@
+httpcheck Goa plugin
+===
+
+This plugin provides a mounter for the [Goa](http://github.com/goadesign/goa) HTTP endpoints, enabling seamless integration with [httpcheck](https://github.com/ikawaha/httpcheck). The mounter satisfies the http.Handler interface, allowing it to be directly set and utilized within httpcheck.
+
+## Usage Example
+
+The [following example](https://github.com/ikawaha/httpcheck/blob/5e434b64049b13f5558e83d26abdeaa28b281cd7/plugin/goa/_test/calc_test.go#L18-L35) demonstrates how to use the goa plugin to test a Goa HTTP endpoint. In this example, we're testing an endpoint that multiplies two numbers.
+
+```go
+package calc
+
+import (
+	"io"
+	"net/http"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/ikawaha/httpcheck"
+	"github.com/ikawaha/httpcheck/plugin/goa"
+	gen "github.com/ikawaha/httpcheck/plugin/goa/calc/gen/calc"
+	"github.com/ikawaha/httpcheck/plugin/goa/calc/gen/http/calc/server"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMounter(t *testing.T) {
+	m := goa.NewMounter()
+	m.Mount(goa.EndpointModular{
+		Builder:  server.NewMultiplyHandler,
+		Mounter:  server.MountMultiplyHandler,
+		Endpoint: gen.NewMultiplyEndpoint(NewCalc()),
+	})
+	httpcheck.New(m).Test(t, "GET", "/multiply/3/5").
+		Check().
+		MustHasStatus(http.StatusOK).
+		Cb(func(r *http.Response) {
+			b, err := io.ReadAll(r.Body)
+			require.NoError(t, err)
+			i, err := strconv.Atoi(strings.TrimSpace(string(b)))
+			assert.NoError(t, err, string(b))
+			assert.Equal(t, 3*5, i)
+		})
+}
+```