feat: entso-e support custom base url

Will be useful for adding smoke tests or integration tests.

Author: piprett

src/sources/entsoe.rs

@@ -21,13 +21,22 @@ pub struct EntsoePriceSource {
 }
 
 impl EntsoePriceSource {
-    pub fn new(api_key: &str) -> Self {
+    /// Creates a new instance of the ENTSO-E price source, with a custom base URL.
+    /// See [EntsoePriceSource::new] to use the default base URL.
+    // Useful for integration testing.
+    pub fn new_with_base_url(api_key: &str, base_url: &str) -> Self {
         EntsoePriceSource {
             api_key: api_key.into(),
-            base_url: "https://web-api.tp.entsoe.eu/".to_string(),
+            base_url: base_url.into(),
         }
     }
 
+    /// Creates a new instance of the ENTSO-E price source.
+    /// See [EntsoePriceSource::new_with_base_url] to use a custom base URL.
+    pub fn new(api_key: &str) -> Self {
+        EntsoePriceSource::new_with_base_url(api_key, "https://web-api.tp.entsoe.eu/")
+    }
+
     /// Gets the API URL used to fetch day-ahead price data from ENTSO-E.
     // https://documenter.getpostman.com/view/7009892/2s93JtP3F6#3b383df0-ada2-49fe-9a50-98b1bb201c6b
     // Beware of awkward time format used by ENTOS-E.
@@ -237,15 +246,12 @@ mod tests {
 
     #[gtest]
     fn test_get_api_url_custom_base() {
-        let url = EntsoePriceSource {
-            api_key: "fake-api-key".to_string(),
-            base_url: "https://example.com/".to_string(),
-        }
-        .get_api_url(
-            DeliveryArea::NO1,
-            Time::date(2025, 12, 29).clock(00, 00, 00),
-            Time::date(2025, 12, 30).clock(00, 00, 00),
-        );
+        let url = EntsoePriceSource::new_with_base_url("fake-api-key", "https://example.com/")
+            .get_api_url(
+                DeliveryArea::NO1,
+                Time::date(2025, 12, 29).clock(00, 00, 00),
+                Time::date(2025, 12, 30).clock(00, 00, 00),
+            );
         expect_that!(
             url,
             eq(