test: add test for getModuleDoc?

tests/lean/moduleDoc.lean

@@ -8,6 +8,14 @@ def tst : MetaM Unit := do
   let docs := getMainModuleDoc (← getEnv)
   IO.println <| docs.toList.map repr
 
+def printDoc (moduleName : Name) : MetaM Unit := do
+  match getModuleDoc? (← getEnv) moduleName with
+  | some docs => IO.println <| docs.toList.map repr
+  | _ => throwError "module not found"
+
 /-! Another module doc. -/
 
 #eval tst
+
+#eval printDoc `Lean.Meta.ReduceEval
+#eval printDoc `Lean.Data.Lsp.Communication

tests/lean/moduleDoc.lean.expected.out

@@ -1 +1,3 @@
 ["Testing module documentation. ", "Another module doc. "]
+["Evaluation by reduction "]
+["Reading/writing LSP messages from/to IO handles. "]