Add some tests around ClientCapabilities

As far as I can tell, there are no tests that depend on any of the
values contained within `ClientCapabilities`. This commit adds some
tests around the construction of the `TextDocumentSyncOptions` field for
the server's capabilities.

It also fixes a bug that was introduced in the previous commit

pygls/capabilities.py

@@ -62,8 +62,7 @@ def get_capability(
         return default
 
     # If we reach the desired leaf value but it's None, return the default.
-    value = default if value is None else value
-    return
+    return default if value is None else value
 
 
 class ServerCapabilitiesBuilder:

tests/test_capabilities.py

@@ -0,0 +1,136 @@
+from typing import Set
+
+import pytest
+from lsprotocol.types import (
+    TEXT_DOCUMENT_DID_OPEN,
+    TEXT_DOCUMENT_DID_CLOSE,
+    TEXT_DOCUMENT_DID_SAVE,
+    TEXT_DOCUMENT_WILL_SAVE,
+    TEXT_DOCUMENT_WILL_SAVE_WAIT_UNTIL,
+    ClientCapabilities,
+    SaveOptions,
+    TextDocumentClientCapabilities,
+    TextDocumentSaveRegistrationOptions,
+    TextDocumentSyncClientCapabilities,
+    TextDocumentSyncKind,
+    TextDocumentSyncOptions,
+)
+
+from pygls.capabilities import ServerCapabilitiesBuilder
+
+
+@pytest.mark.parametrize("capabilities,features,options,expected", [
+
+    # textDocument/didOpen
+    (
+        ClientCapabilities(),
+        set(),
+        {},
+        TextDocumentSyncOptions(
+            open_close=False,
+            change=TextDocumentSyncKind.Incremental,
+            save=False,
+        )
+    ),
+    (
+        ClientCapabilities(),
+        {TEXT_DOCUMENT_DID_OPEN},
+        {},
+        TextDocumentSyncOptions(
+            open_close=True,
+            change=TextDocumentSyncKind.Incremental,
+            save=False,
+        )
+    ),
+    (
+        ClientCapabilities(),
+        {TEXT_DOCUMENT_DID_CLOSE},
+        {},
+        TextDocumentSyncOptions(
+            open_close=True,
+            change=TextDocumentSyncKind.Incremental,
+            save=False,
+        )
+    ),
+    # textDocument/willSave & textDocument/willSaveWaitUntil
+    (
+        ClientCapabilities(),
+        {TEXT_DOCUMENT_WILL_SAVE},
+        {},
+        TextDocumentSyncOptions(
+            open_close=False,
+            change=TextDocumentSyncKind.Incremental,
+            save=False,
+        )
+    ),
+    (
+        ClientCapabilities(
+            text_document=TextDocumentClientCapabilities(
+                synchronization=TextDocumentSyncClientCapabilities(
+                    will_save=True
+                )
+            )
+        ),
+        {TEXT_DOCUMENT_WILL_SAVE},
+        {},
+        TextDocumentSyncOptions(
+            open_close=False,
+            change=TextDocumentSyncKind.Incremental,
+            save=False,
+            will_save=True
+        )
+    ),
+    (
+        ClientCapabilities(
+            text_document=TextDocumentClientCapabilities(
+                synchronization=TextDocumentSyncClientCapabilities(
+                    will_save_wait_until=True
+                )
+            )
+        ),
+        {TEXT_DOCUMENT_WILL_SAVE_WAIT_UNTIL},
+        {},
+        TextDocumentSyncOptions(
+            open_close=False,
+            change=TextDocumentSyncKind.Incremental,
+            save=False,
+            will_save_wait_until=True
+        )
+    ),
+    # textDocument/didSave
+    (
+        ClientCapabilities(),
+        {TEXT_DOCUMENT_DID_SAVE},
+        {},
+        TextDocumentSyncOptions(
+            open_close=False,
+            change=TextDocumentSyncKind.Incremental,
+            save=True,
+        )
+    ),
+    (
+        ClientCapabilities(),
+        {TEXT_DOCUMENT_DID_SAVE},
+        {TEXT_DOCUMENT_DID_SAVE: TextDocumentSaveRegistrationOptions(include_text=True)},
+        TextDocumentSyncOptions(
+            open_close=False,
+            change=TextDocumentSyncKind.Incremental,
+            save=SaveOptions(include_text=True),
+        )
+    )
+])
+def test_text_doc_sync_capabilities(
+    capabilities: ClientCapabilities,
+    features: Set[str],
+    options,
+    expected: TextDocumentSyncOptions
+):
+    """Ensure that `pygls` can correctly construct server capabilities for the
+    text document sync features."""
+
+    builder = ServerCapabilitiesBuilder(
+        capabilities, features, options, [], TextDocumentSyncKind.Incremental
+    )
+
+    actual = builder.build().text_document_sync
+    assert expected == actual