Install sxs with the install-dotnet scripts (#124)

* Use dotnet-install scripts for proper sxs

* Update dotnet version in testing

* Error message cleanup

* SxS testing in the dotnet project

* Update package lock

* Test fixes

* Use proper environment variable

* Set dotnet root for windows

__tests__/setup-dotnet.test.ts

@@ -0,0 +1,48 @@
+import io = require('@actions/io');
+import fs = require('fs');
+import os = require('os');
+import path = require('path');
+
+const toolDir = path.join(__dirname, 'runner', 'tools2');
+const tempDir = path.join(__dirname, 'runner', 'temp2');
+
+import * as setup from '../src/setup-dotnet';
+
+const IS_WINDOWS = process.platform === 'win32';
+
+describe('setup-dotnet tests', () => {
+  beforeAll(async () => {
+    process.env.RUNNER_TOOL_CACHE = toolDir;
+    process.env.DOTNET_INSTALL_DIR = toolDir;
+    process.env.RUNNER_TEMP = tempDir;
+    await io.rmRF(toolDir);
+    await io.rmRF(tempDir);
+  });
+
+  afterAll(async () => {
+    try {
+      await io.rmRF(path.join(process.cwd(), 'global.json'));
+      await io.rmRF(toolDir);
+      await io.rmRF(tempDir);
+    } catch {
+      console.log('Failed to remove test directories');
+    }
+  }, 30000);
+
+  it('Acquires version of dotnet if no matching version is installed', async () => {
+    const globalJsonPath = path.join(process.cwd(), 'global.json');
+    const jsonContents = `{${os.EOL}"sdk": {${os.EOL}"version": "3.1.201"${os.EOL}}${os.EOL}}`;
+    if (!fs.existsSync(globalJsonPath)) {
+      fs.writeFileSync(globalJsonPath, jsonContents);
+    }
+    await setup.run();
+
+    expect(fs.existsSync(path.join(toolDir, 'sdk', '3.1.201'))).toBe(true);
+    if (IS_WINDOWS) {
+      expect(fs.existsSync(path.join(toolDir, 'dotnet.exe'))).toBe(true);
+    } else {
+      expect(fs.existsSync(path.join(toolDir, 'dotnet'))).toBe(true);
+    }
+    fs.unlinkSync(globalJsonPath);
+  }, 100000);
+});