test: add integration tests

tests/from_file.rs

@@ -0,0 +1,111 @@
+use filecaster::FromFile;
+
+#[derive(Debug, Clone, PartialEq, FromFile)]
+struct Simple {
+    x: i32,
+    #[from_file(default = "hello")]
+    y: String,
+}
+
+#[derive(Debug, Clone, PartialEq, FromFile)]
+struct NumericDefault {
+    a: i32,
+    #[from_file(default = 42)]
+    b: i32,
+}
+
+#[test]
+fn test_simple_defaults() {
+    // No file passed -> all fields fall back to defaults
+    let s = Simple::from_file(None);
+    assert_eq!(
+        s,
+        Simple {
+            x: 0,
+            y: "hello".to_string(),
+        }
+    );
+}
+
+#[test]
+fn test_simple_override() {
+    // Manually construct the generated `SimpleFile` and override both fields
+    let file = SimpleFile {
+        x: Some(10),
+        y: Some("world".to_string()),
+    };
+    let s = Simple::from_file(Some(file));
+    assert_eq!(
+        s,
+        Simple {
+            x: 10,
+            y: "world".to_string(),
+        }
+    );
+}
+
+#[test]
+fn test_simple_serde_empty() {
+    // Deserialize from JSON missing both fields -> both None
+    let json = "{}";
+    let file: SimpleFile = serde_json::from_str(json).unwrap();
+    let s = Simple::from_file(Some(file));
+    assert_eq!(s.x, 0);
+    assert_eq!(s.y, "hello".to_string());
+}
+
+#[test]
+fn test_simple_serde_partial() {
+    // Deserialize from JSON with only `x`
+    let json = r#"{"x":5}"#;
+    let file: SimpleFile = serde_json::from_str(json).unwrap();
+    let s = Simple::from_file(Some(file));
+    assert_eq!(s.x, 5);
+    assert_eq!(s.y, "hello".to_string());
+}
+
+#[test]
+fn test_simple_serde_full() {
+    // Deserialize from JSON with both fields
+    let json = r#"{"x":7,"y":"rust"}"#;
+    let file: SimpleFile = serde_json::from_str(json).unwrap();
+    let s = Simple::from_file(Some(file));
+    assert_eq!(s.x, 7);
+    assert_eq!(s.y, "rust".to_string());
+}
+
+#[test]
+fn test_numeric_default() {
+    // No file -> default `b = 42`
+    let n = NumericDefault::from_file(None);
+    assert_eq!(n, NumericDefault { a: 0, b: 42 });
+
+    // Override both
+    let file = NumericDefaultFile {
+        a: Some(7),
+        b: Some(99),
+    };
+    let n2 = NumericDefault::from_file(Some(file));
+    assert_eq!(n2, NumericDefault { a: 7, b: 99 });
+}
+
+#[cfg(feature = "merge")]
+mod merge_tests {
+    use super::*;
+    use merge::Merge;
+
+    #[test]
+    fn test_merge_simple_file() {
+        let mut f1 = SimpleFile {
+            x: Some(1),
+            y: None,
+        };
+        let f2 = SimpleFile {
+            x: None,
+            y: Some("foo".to_string()),
+        };
+        f1.merge(f2);
+        assert_eq!(f1.x, Some(1));
+        assert_eq!(f1.y, Some("foo".to_string()));
+    }
+}