add some more tests

tests/assn.matzo

@@ -0,0 +1,2 @@
+x := 5;
+y := This;

tests/assn.parsed

@@ -0,0 +1,18 @@
+[
+    Assn(
+        "x",
+        Lit(
+            Num(
+                5,
+            ),
+        ),
+    ),
+    Assn(
+        "y",
+        Lit(
+            Atom(
+                "This",
+            ),
+        ),
+    ),
+]

tests/atom_lit.matzo

@@ -0,0 +1 @@
+puts Foo

tests/atom_lit.parsed

@@ -0,0 +1,9 @@
+[
+    Puts(
+        Lit(
+            Atom(
+                "Foo",
+            ),
+        ),
+    ),
+]