Handle undefined result from executeDocumentSymbolProvider (#39)

When resolving test symbols in a document, it's possible that there are
situations where the call to get document symbols will return undefined
(mainly if language server is still activating). This was resulting in
an uncaught exception that causes the loading to appear "stuck" on the
UI. This adds correct handling if this result is undefined.

Author: mnoah1

src/language-tools/python.ts

@@ -97,7 +97,7 @@ export class PythonLanguageTools
     }
 
     // Document symbols provided by Pylance.
-    const symbols: vscode.DocumentSymbol[] =
+    const symbols: vscode.DocumentSymbol[] | undefined =
       await vscode.commands.executeCommand(
         'vscode.executeDocumentSymbolProvider',
         document
@@ -161,8 +161,10 @@ export class PythonLanguageTools
     }
 
     // Start at top level and evaluate each symbol in the document.
-    for (const symbol of symbols) {
-      evaluateCurrentSymbol(symbol)
+    if (symbols) {
+      for (const symbol of symbols) {
+        evaluateCurrentSymbol(symbol)
+      }
     }
 
     const finalTestCases = result.filter(item => {

src/test/suite/language-tools/python.test.ts

@@ -78,6 +78,16 @@ suite('Python Language Tools', () => {
     assert.equal(result.documentTest?.name, 'my_test.py')
   })
 
+  test('undefined symbols', async () => {
+    executeCommandStub.resolves(undefined)
+    const result = await languageTools.getDocumentTestCases(
+      vscode.Uri.parse('file:///repo/root/sample/my_test.py'),
+      '/repo/root/'
+    )
+    assert.strictEqual(result.isTestFile, true)
+    assert.strictEqual(result.testCases.length, 0)
+  })
+
   test('non test file', async () => {
     const result = await languageTools.getDocumentTestCases(
       vscode.Uri.parse('file:///repo/root/sample/my_file.py'),