test: test for config file creation and default config file parsing (#459)

.github/workflows/test.yaml

@@ -57,3 +57,10 @@ jobs:
           # token: ${{ secrets.CODECOV_TOKEN }}
           files: ./lcov.info
           fail_ci_if_error: true
+      - name: Test creation of config file
+        run: |
+          CONFIG_PATH=~/.config/topgrade.toml;
+          if [ -f "$CONFIG_PATH" ]; then rm $CONFIG_PATH; fi
+          cargo build; 
+          ./target/debug/topgrade --dry-run --only system;
+          stat $CONFIG_PATH;

src/config.rs

@@ -1515,3 +1515,16 @@ impl Config {
         self.opt.custom_commands.iter().any(|s| s == name)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use crate::config::ConfigFile;
+
+    /// Test the default configuration in `config.example.toml` is valid.
+    #[test]
+    fn test_default_config() {
+        let str = include_str!("../config.example.toml");
+
+        assert!(toml::from_str::<ConfigFile>(str).is_ok());
+    }
+}