[8.19] (backport #11605) Convert readDocker in package tests to a testing helper to get more specific errors (#11624)

* Convert readDocker to testing helper. (#11605)

(cherry picked from commit 57d2faa)

# Conflicts:
#	dev-tools/packaging/testing/package_test.go

* Fix conflicts

---------

Co-authored-by: Craig MacKenzie <[email protected]>

Author: mergify[bot]

dev-tools/packaging/testing/package_test.go

@@ -372,7 +372,7 @@ func checkNpcapNotices(pkg, file string, contents io.Reader) error {
 }
 
 func checkDocker(t *testing.T, file string, fipsPackage bool) {
-	p, info, err := readDocker(file, true)
+	p, info, err := readDocker(t, file, true)
 	if err != nil {
 		t.Errorf("error reading file %v: %v", file, err)
 		return
@@ -398,7 +398,7 @@ func checkDocker(t *testing.T, file string, fipsPackage bool) {
 }
 
 func checkCompleteDocker(t *testing.T, file string) {
-	p, _, err := readDocker(file, false)
+	p, _, err := readDocker(t, file, false)
 	if err != nil {
 		t.Errorf("error reading file %v: %v", file, err)
 	}
@@ -977,27 +977,23 @@ func openZip(zipFile string) (*zip.ReadCloser, error) {
 	return r, nil
 }
 
-func readDocker(dockerFile string, filterWorkingDir bool) (*packageFile, *dockerInfo, error) {
+func readDocker(t *testing.T, dockerFile string, filterWorkingDir bool) (*packageFile, *dockerInfo, error) {
+	t.Helper()
+
 	// Read the manifest file first so that the config file and layer
 	// names are known in advance.
 	manifest, err := getDockerManifest(dockerFile)
-	if err != nil {
-		return nil, nil, err
-	}
+	require.NoError(t, err)
 
 	file, err := os.Open(dockerFile)
-	if err != nil {
-		return nil, nil, err
-	}
+	require.NoError(t, err)
 	defer file.Close()
 
 	var info *dockerInfo
 	layers := make(map[string]*packageFile)
 
 	gzipReader, err := gzip.NewReader(file)
-	if err != nil {
-		return nil, nil, err
-	}
+	require.NoError(t, err)
 	defer gzipReader.Close()
 
 	tarReader := tar.NewReader(gzipReader)
@@ -1007,38 +1003,29 @@ func readDocker(dockerFile string, filterWorkingDir bool) (*packageFile, *docker
 			if errors.Is(err, io.EOF) {
 				break
 			}
-			return nil, nil, err
+			require.NoError(t, err)
 		}
 
 		switch {
 		case header.Name == manifest.Config:
 			info, err = readDockerInfo(tarReader)
-			if err != nil {
-				return nil, nil, err
-			}
+			require.NoError(t, err)
 		case slices.Contains(manifest.Layers, header.Name):
 			layer, err := readTarContents(header.Name, tarReader)
-			if err != nil {
-				return nil, nil, err
-			}
+			require.NoError(t, err)
 			layers[header.Name] = layer
 		}
 	}
 
-	if len(info.Config.Entrypoint) == 0 {
-		return nil, nil, fmt.Errorf("no entrypoint")
-	}
-
+	require.NotZero(t, len(info.Config.Entrypoint), "no entrypoint")
 	workingDir := info.Config.WorkingDir
 	entrypoint := info.Config.Entrypoint[0]
 
 	// Read layers in order and for each file keep only the entry seen in the later layer
 	p := &packageFile{Name: filepath.Base(dockerFile), Contents: map[string]packageEntry{}}
 	for _, layer := range manifest.Layers {
 		layerFile, found := layers[layer]
-		if !found {
-			return nil, nil, fmt.Errorf("layer not found: %s", layer)
-		}
+		require.True(t, found, fmt.Sprintf("layer not found: %s", layer))
 		for name, entry := range layerFile.Contents {
 			if excludedPathsPattern.MatchString(name) {
 				continue
@@ -1056,10 +1043,7 @@ func readDocker(dockerFile string, filterWorkingDir bool) (*packageFile, *docker
 		}
 	}
 
-	if len(p.Contents) == 0 {
-		return nil, nil, fmt.Errorf("no files found in docker working directory (%s)", info.Config.WorkingDir)
-	}
-
+	require.NotZero(t, len(p.Contents), fmt.Sprintf("no files found in docker working directory (%s)", info.Config.WorkingDir))
 	return p, info, nil
 }