Split decompressDir from runDecompressDirs

... so that we have a new function which only decompresses
one image at a time.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

integration/utils.go

@@ -194,19 +194,25 @@ func runDecompressDirs(t *testing.T, args ...string) {
 		m, err := os.ReadFile(filepath.Join(dir, "manifest.json"))
 		require.NoError(t, err)
 		t.Logf("manifest %d before: %s", i+1, string(m))
-	}
+
-	out, err := exec.Command(decompressDirsBinary, args...).CombinedOutput()
+		decompressDir(t, dir)
-	assert.NoError(t, err, "%s", out)
+
-	for i, dir := range args {
+		m, err = os.ReadFile(filepath.Join(dir, "manifest.json"))
-		if len(out) > 0 {
-			t.Logf("output: %s", out)
-		}
-		m, err := os.ReadFile(filepath.Join(dir, "manifest.json"))
 		require.NoError(t, err)
 		t.Logf("manifest %d after: %s", i+1, string(m))
 	}
 }
 
+// decompressDir modifies a dir:-formatted directory to replace gzip-compressed layers with uncompressed variants,
+// and to use a ~canonical formatting of manifest.json.
+func decompressDir(t *testing.T, dir string) {
+	out, err := exec.Command(decompressDirsBinary, dir).CombinedOutput()
+	assert.NoError(t, err, "%s", out)
+	if len(out) > 0 {
+		t.Logf("output: %s", out)
+	}
+}
+
 // Verify manifest in a dir: image at dir is expectedMIMEType.
 func verifyManifestMIMEType(t *testing.T, dir string, expectedMIMEType string) {
 	manifestBlob, err := os.ReadFile(filepath.Join(dir, "manifest.json"))