tests/unix/extra_coverage: Add basic tests to import frozen str and mpy.

tests/unix/extra_coverage.py

@@ -13,3 +13,7 @@ print(hash(data[0]))
 print(hash(data[1]))
 print(hash(bytes(data[0], 'utf8')))
 print(hash(str(data[1], 'utf8')))
+
+# test basic import of frozen scripts
+import frzstr1
+import frzmpy1

tests/unix/extra_coverage.py.exp

@@ -48,3 +48,5 @@ Warning: test
 7300
 7300
 7300
+frzstr1
+frzmpy1