test(sidecar): split tests across stub and withsidecar builds

Default !withsidecar build: assert IsPlaceholder, empty JAR,
Extract errors. withsidecar build: existing extract/checksum
coverage.

internal/sidecar/embed_withsidecar_test.go

@@ -0,0 +1,90 @@
+//go:build withsidecar
+
+package sidecar
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestEmbeddedNonZero(t *testing.T) {
+	if EmbeddedSize() == 0 {
+		t.Errorf("expected embedded JAR to be non-empty")
+	}
+	if IsPlaceholder() {
+		t.Errorf("withsidecar build should not be a placeholder")
+	}
+}
+
+func TestExtract_WritesJARAndChecksum(t *testing.T) {
+	directory := t.TempDir()
+	path, err := Extract(directory)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if path != filepath.Join(directory, "uatu-sidecar.jar") {
+		t.Errorf("unexpected path: %s", path)
+	}
+	body, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if EmbeddedSize() != len(body) {
+		t.Errorf("size mismatch: embedded=%d, written=%d", EmbeddedSize(), len(body))
+	}
+	sum := sha256.Sum256(body)
+	if hex.EncodeToString(sum[:]) != EmbeddedSHA256() {
+		t.Errorf("hash mismatch")
+	}
+	checksum, err := os.ReadFile(path + ".sha256")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(checksum) != EmbeddedSHA256() {
+		t.Errorf("checksum file content wrong: %q", checksum)
+	}
+}
+
+func TestExtract_ReusesIdenticalFile(t *testing.T) {
+	directory := t.TempDir()
+	path, err := Extract(directory)
+	if err != nil {
+		t.Fatal(err)
+	}
+	originalStat, err := os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	originalModTime := originalStat.ModTime()
+
+	if _, err := Extract(directory); err != nil {
+		t.Fatal(err)
+	}
+	secondStat, err := os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !secondStat.ModTime().Equal(originalModTime) {
+		t.Errorf("second extract should not have rewritten the file")
+	}
+}
+
+func TestExtract_RewritesIfChecksumMissing(t *testing.T) {
+	directory := t.TempDir()
+	path, err := Extract(directory)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Remove(path + ".sha256"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := Extract(directory); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(path + ".sha256"); err != nil {
+		t.Errorf("checksum should have been written: %v", err)
+	}
+}