Use an auto-generated pub snapshot for tests.

lib/src/git.dart

Index: lib/src/git.dart
diff --git a/lib/src/git.dart b/lib/src/git.dart
index 53d69d89f3d6012776888d85db5beea3a0148a17..f2c2c226416453c4ea502e343738c683a7661d71 100644
--- a/lib/src/git.dart
+++ b/lib/src/git.dart
@@ -76,6 +76,18 @@ List<String> runSync(List<String> args, {String workingDir,
   return result.stdout;
 }
 
+/// Starts a git process and returns it.
+Future<PubProcess> start(List<String> args,
+    {String workingDir, Map<String, String> environment}) {
+  if (!isInstalled) {
+    fail("Cannot find a Git executable.\n"
+        "Please ensure Git is correctly installed.");
+  }
+
+  return startProcess(_gitCommand, args, workingDir: workingDir,
+      environment: environment);
+}
+
 /// Returns the name of the git command-line app, or null if Git could not be
 /// found on the user's PATH.
 String get _gitCommand {