Add a basic test for dynamic linking

dynamic/.gitignore

@@ -0,0 +1 @@
+/plugin.so

dynamic/dynamic_test.go

@@ -0,0 +1,46 @@
+// +build linux darwin
+
+package main
+
+import (
+	"bytes"
+	"log"
+	"os/exec"
+	"plugin"
+	"testing"
+)
+
+// This is a cursory test that checks whether things work under dynamic linking.
+
+func TestMain(m *testing.M) {
+	cmd := exec.Command(
+		"go", "build",
+		"-buildmode", "plugin",
+		"-o", "plugin.so",
+		"plugin.go",
+	)
+	var out bytes.Buffer
+	cmd.Stdout = &out
+	cmd.Stderr = &out
+	if err := cmd.Run(); err != nil {
+		log.Fatalf("Error building plugin: %s\nOutput:\n%s", err, out.String())
+	}
+	m.Run()
+}
+
+func TestDynamic(t *testing.T) {
+	plug, err := plugin.Open("plugin.so")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, test := range []string{
+		"TestSum",
+		"TestDigest",
+	} {
+		f, err := plug.Lookup(test)
+		if err != nil {
+			t.Fatalf("cannot find func %s: %s", test, err)
+		}
+		f.(func(*testing.T))(t)
+	}
+}

dynamic/plugin.go

@@ -0,0 +1,46 @@
+// +build ignore
+
+package main
+
+import (
+	"fmt"
+	"log"
+	"testing"
+
+	"github.com/cespare/xxhash/v2"
+)
+
+const (
+	in   = "Call me Ishmael. Some years ago--never mind how long precisely-"
+	want = 0x02a2e85470d6fd96
+)
+
+func TestSum(t *testing.T) {
+	got := xxhash.Sum64String(in)
+	if got != want {
+		t.Fatalf("Sum64String: got 0x%x; want 0x%x", got, want)
+	}
+}
+
+func TestDigest(t *testing.T) {
+	for chunkSize := 1; chunkSize <= len(in); chunkSize++ {
+		name := fmt.Sprintf("[chunkSize=%d]", chunkSize)
+		t.Run(name, func(t *testing.T) {
+			d := xxhash.New()
+			for i := 0; i < len(in); i += chunkSize {
+				chunk := in[i:]
+				if len(chunk) > chunkSize {
+					chunk = chunk[:chunkSize]
+				}
+				n, err := d.WriteString(chunk)
+				if err != nil || n != len(chunk) {
+					t.Fatalf("Digest.WriteString: got (%d, %v); want (%d, nil)",
+						n, err, len(chunk))
+				}
+			}
+			if got := d.Sum64(); got != want {
+				log.Fatalf("Digest.Sum64: got 0x%x; want 0x%x", got, want)
+			}
+		})
+	}
+}