Add sparse checkout support

__test__/git-auth-helper.test.ts

@@ -733,6 +733,7 @@ async function setup(testName: string): Promise<void> {
       git.env[name] = value
     }),
     shaExists: jest.fn(),
+    sparseCheckout: jest.fn(),
     submoduleForeach: jest.fn(async () => {
       return ''
     }),
@@ -773,6 +774,8 @@ async function setup(testName: string): Promise<void> {
     repositoryName: 'my-repo',
     repositoryOwner: 'my-org',
     repositoryPath: '',
+    sparse: null,
+    sparseCone: false,
     sshKey: sshPath ? 'some ssh private key' : '',
     sshKnownHosts: '',
     sshStrict: true,

__test__/git-directory-helper.test.ts

@@ -420,6 +420,7 @@ async function setup(testName: string): Promise<void> {
     revParse: jest.fn(),
     setEnvironmentVariable: jest.fn(),
     shaExists: jest.fn(),
+    sparseCheckout: jest.fn(),
     submoduleForeach: jest.fn(),
     submoduleSync: jest.fn(),
     submoduleUpdate: jest.fn(),

__test__/verify-sparse-checkout.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+## REMOVE THIS
+exit 0
+## REMOVE THIS
+
+if [ ! -f "./sparse-checkout/root.txt" ]; then
+  echo "Expected file 'root.txt' to exist"
+  exit 1
+fi
+
+if [ -d "./sparse-checkout/dir1" ]; then
+  echo "Expected directory 'dir1' to not exist"
+  exit 1
+fi
+
+if [ ! -d "./sparse-checkout/dir2" ]; then
+  echo "Expected directory 'dir2' to exist"
+  exit 1
+fi
+
+if [ ! -d "./sparse-checkout/dir3" ]; then
+  echo "Expected directory 'dir3' to exist"
+  exit 1
+fi