Add test for export of GOROOT to env var

Signed-off-by: Manuel Mendez <mmendez534@gmail.com>

__tests__/setup-go.test.ts

@@ -45,6 +45,7 @@ describe('setup-go', () => {
     inputs = {};
     inSpy = jest.spyOn(core, 'getInput');
     inSpy.mockImplementation(name => inputs[name]);
+    exSpy = jest.spyOn(core, 'exportVariable');
 
     // node
     os = {};
@@ -229,6 +230,22 @@ describe('setup-go', () => {
     expect(logSpy).toHaveBeenCalledWith(`Setup go stable version spec 1.13.0`);
   });
 
+  it('exports GOROOT', async () => {
+    inputs['go-version'] = '1.13.0';
+    inSpy.mockImplementation(name => inputs[name]);
+
+    let toolPath = path.normalize('/cache/go/1.13.0/x64');
+    findSpy.mockImplementation(() => toolPath);
+
+    let vars = {} as any;
+    exSpy.mockImplementation(async(name, val) => {
+      vars[name] = val
+    });
+
+    await main.run();
+    expect(vars).toBe({'GOROOT': 'foo'});
+  });
+
   it('finds a version of go already in the cache', async () => {
     inputs['go-version'] = '1.13.0';