Add basic preprocessor test

tests/test_preprocessor.py

@@ -0,0 +1,27 @@
+from cxxheaderparser.options import ParserOptions
+from cxxheaderparser.preprocessor import make_pcpp_preprocessor
+from cxxheaderparser.simple import NamespaceScope, ParsedData, parse_string
+from cxxheaderparser.types import FundamentalSpecifier, NameSpecifier, PQName, Token, Type, Value, Variable
+
+
+def test_basic_preprocessor() -> None:
+    content = """
+      #define X 1
+      int x = X;
+    """
+    options = ParserOptions(preprocessor=make_pcpp_preprocessor())
+    data = parse_string(content, cleandoc=True, options=options)
+
+    assert data == ParsedData(
+        namespace=NamespaceScope(
+            variables=[
+                Variable(
+                    name=PQName(segments=[NameSpecifier(name="x")]),
+                    type=Type(
+                        typename=PQName(segments=[FundamentalSpecifier(name="int")])
+                    ),
+                    value=Value(tokens=[Token(value="1")]),
+                )
+            ]
+        )
+    )