diff --git a/crates/nuncio-cal/Cargo.toml b/crates/nuncio-cal/Cargo.toml
index 22bb938..4c7e3c1 100644
--- a/crates/nuncio-cal/Cargo.toml
+++ b/crates/nuncio-cal/Cargo.toml
@@ -20,4 +20,9 @@ chrono.workspace = true
 reqwest.workspace = true
 quick-xml.workspace = true
 
+[dev-dependencies]
+tempfile.workspace = true
+wiremock.workspace = true
+
+
 
diff --git a/crates/nuncio-cal/src/lib.rs b/crates/nuncio-cal/src/lib.rs
index 6ec3c23..d06b962 100644
--- a/crates/nuncio-cal/src/lib.rs
+++ b/crates/nuncio-cal/src/lib.rs
@@ -1,9 +1,11 @@
 //! iCalendar (RFC 5545), CalDAV (RFC 4791), and recurrence engine for Nuncio.
 
 pub mod caldav;
+pub mod mock;
 pub mod parser;
 pub mod rrule;
 
 pub use caldav::CalDavClient;
+pub use mock::MockCalendarBackend;
 pub use parser::{CalendarError, IcalParserAdapter};
 pub use rrule::RecurrenceEngine;
diff --git a/crates/nuncio-cal/src/mock.rs b/crates/nuncio-cal/src/mock.rs
new file mode 100644
index 0000000..8ba7a02
--- /dev/null
+++ b/crates/nuncio-cal/src/mock.rs
@@ -0,0 +1,129 @@
+//! Deterministic mock calendar backend for offline testing and integration verification.
+
+use nuncio_core::model::CalendarEvent;
+use std::sync::{Arc, Mutex};
+
+use crate::parser::CalendarError;
+
+/// Thread-safe mock calendar backend for offline testing.
+#[derive(Debug, Clone, Default)]
+pub struct MockCalendarBackend {
+    events: Arc<Mutex<Vec<CalendarEvent>>>,
+    should_fail: Arc<Mutex<bool>>,
+}
+
+impl MockCalendarBackend {
+    /// Create a new `MockCalendarBackend`.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Configure the mock to simulate network failure errors.
+    pub fn set_should_fail(&self, fail: bool) {
+        if let Ok(mut flag) = self.should_fail.lock() {
+            *flag = fail;
+        }
+    }
+
+    /// Add a mock calendar event to storage.
+    pub fn add_event(&self, event: CalendarEvent) {
+        if let Ok(mut guard) = self.events.lock() {
+            guard.push(event);
+        }
+    }
+
+    /// Retrieve calendar events for a specific calendar collection within a time window.
+    pub fn list_events(
+        &self,
+        calendar_id: &str,
+        start_window: i64,
+        end_window: i64,
+    ) -> Result<Vec<CalendarEvent>, CalendarError> {
+        if *self.should_fail.lock().unwrap() {
+            return Err(CalendarError::ParseFailed(
+                "simulated CalDAV network failure".to_string(),
+            ));
+        }
+
+        let guard = self.events.lock().unwrap();
+        let matches = guard
+            .iter()
+            .filter(|e| e.calendar_id == calendar_id && e.start_time >= start_window && e.end_time <= end_window)
+            .cloned()
+            .collect();
+
+        Ok(matches)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use wiremock::matchers::{method, path};
+    use wiremock::{Mock, MockServer, ResponseTemplate};
+
+    #[test]
+    fn mock_calendar_backend_operations() {
+        let mock = MockCalendarBackend::new();
+        let event = CalendarEvent {
+            id: "evt-m1".to_string(),
+            account_id: "acct-1".to_string(),
+            calendar_id: "cal-work".to_string(),
+            summary: "Mock Planning".to_string(),
+            start_time: 1700000000,
+            end_time: 1700003600,
+            rrule: None,
+            location: None,
+        };
+        mock.add_event(event.clone());
+
+        let events = mock
+            .list_events("cal-work", 1699999000, 1700004000)
+            .expect("list events succeeds");
+        assert_eq!(events.len(), 1);
+        assert_eq!(events[0].id, "evt-m1");
+
+        mock.set_should_fail(true);
+        assert!(mock.list_events("cal-work", 1699999000, 1700004000).is_err());
+    }
+
+    #[tokio::test]
+    async fn wiremock_caldav_report_simulation() {
+        let mock_server = MockServer::start().await;
+
+        let xml_response = r#"<?xml version="1.0" encoding="utf-8"?>
+        <d:multistatus xmlns:d="DAV:" xmlns:c="urn:ietf:params:xml:ns:caldav">
+            <d:response>
+                <d:href>/calendars/work/evt.ics</d:href>
+                <d:propstat>
+                    <d:prop>
+                        <c:calendar-data>BEGIN:VCALENDAR
+VERSION:2.0
+BEGIN:VEVENT
+SUMMARY:Wiremock Event
+END:VEVENT
+END:VCALENDAR</c:calendar-data>
+                    </d:prop>
+                </d:propstat>
+            </d:response>
+        </d:multistatus>"#;
+
+        Mock::given(method("REPORT"))
+            .and(path("/calendars/work/"))
+            .respond_with(ResponseTemplate::new(207).set_body_string(xml_response))
+            .mount(&mock_server)
+            .await;
+
+        let client = reqwest::Client::new();
+        let resp = client
+            .request(
+                reqwest::Method::from_bytes(b"REPORT").unwrap(),
+                format!("{}/calendars/work/", mock_server.uri()),
+            )
+            .send()
+            .await
+            .unwrap();
+
+        assert_eq!(resp.status(), 207);
+    }
+}