url-helper.ts now leverages well-known environment variables. (#1941)

* `utl-helper.ts` now leverages well-known environment variables.

---------
Co-authored-by: Erez Testiler <easyt@github.com>

__test__/url-helper.test.ts

@@ -0,0 +1,55 @@
+import * as urlHelper from '../src/url-helper'
+
+describe('getServerUrl tests', () => {
+  it('basics', async () => {
+    // Note that URL::toString will append a trailing / when passed just a domain name ...
+    expect(urlHelper.getServerUrl().toString()).toBe('https://github.com/')
+    expect(urlHelper.getServerUrl(' ').toString()).toBe('https://github.com/')
+    expect(urlHelper.getServerUrl('   ').toString()).toBe('https://github.com/')
+    expect(urlHelper.getServerUrl('http://contoso.com').toString()).toBe(
+      'http://contoso.com/'
+    )
+    expect(urlHelper.getServerUrl('https://contoso.com').toString()).toBe(
+      'https://contoso.com/'
+    )
+    expect(urlHelper.getServerUrl('https://contoso.com/').toString()).toBe(
+      'https://contoso.com/'
+    )
+
+    // ... but can't make that same assumption when passed an URL that includes some deeper path.
+    expect(urlHelper.getServerUrl('https://contoso.com/a/b').toString()).toBe(
+      'https://contoso.com/a/b'
+    )
+  })
+})
+
+describe('isGhes tests', () => {
+  it('basics', async () => {
+    expect(urlHelper.isGhes()).toBeFalsy()
+    expect(urlHelper.isGhes('https://github.com')).toBeFalsy()
+    expect(urlHelper.isGhes('https://contoso.ghe.com')).toBeFalsy()
+    expect(urlHelper.isGhes('https://test.github.localhost')).toBeFalsy()
+    expect(urlHelper.isGhes('https://src.onpremise.fabrikam.com')).toBeTruthy()
+  })
+})
+
+describe('getServerApiUrl tests', () => {
+  it('basics', async () => {
+    expect(urlHelper.getServerApiUrl()).toBe('https://api.github.com')
+    expect(urlHelper.getServerApiUrl('https://github.com')).toBe(
+      'https://api.github.com'
+    )
+    expect(urlHelper.getServerApiUrl('https://GitHub.com')).toBe(
+      'https://api.github.com'
+    )
+    expect(urlHelper.getServerApiUrl('https://contoso.ghe.com')).toBe(
+      'https://api.contoso.ghe.com'
+    )
+    expect(urlHelper.getServerApiUrl('https://fabrikam.GHE.COM')).toBe(
+      'https://api.fabrikam.ghe.com'
+    )
+    expect(
+      urlHelper.getServerApiUrl('https://src.onpremise.fabrikam.com')
+    ).toBe('https://src.onpremise.fabrikam.com/api/v3')
+  })
+})