feat: add tests and assert coverage (#71)

### Explanation

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### Issue

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### Attestations

- [ ] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [ ] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
- [ ] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [ ] I have pinned the dependencies to a specific patch version.

### Style

- [ ] I have run the linter and resolved any errors.
- [ ] My pull request uses an appropriate title, matching the conventional commit standards.
- [ ] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request.

### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [ ] All new and existing tests pass locally with my changes.
- [ ] Code coverage remains at or above the configured threshold.

### Documentation

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### Versioning

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Co-authored-by: Hikari <hikari@nhcarrigan.com>
Reviewed-on: #71
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src-tauri/src/clipboard.rs

@@ -257,3 +257,468 @@ pub fn update_clipboard_language(
     save_history(&app, &history)?;
     Ok(updated_entry)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // ==================== ClipboardEntry tests ====================
+
+    #[test]
+    fn test_clipboard_entry_new() {
+        let entry = ClipboardEntry::new(
+            "let x = 42;".to_string(),
+            Some("rust".to_string()),
+            Some("main.rs".to_string()),
+        );
+
+        assert_eq!(entry.content, "let x = 42;");
+        assert_eq!(entry.language, Some("rust".to_string()));
+        assert_eq!(entry.source, Some("main.rs".to_string()));
+        assert!(!entry.is_pinned);
+        assert!(!entry.id.is_empty());
+        assert!(!entry.timestamp.is_empty());
+    }
+
+    #[test]
+    fn test_clipboard_entry_new_without_optional_fields() {
+        let entry = ClipboardEntry::new("some content".to_string(), None, None);
+
+        assert_eq!(entry.content, "some content");
+        assert!(entry.language.is_none());
+        assert!(entry.source.is_none());
+        assert!(!entry.is_pinned);
+    }
+
+    #[test]
+    fn test_clipboard_entry_unique_ids() {
+        let entry1 = ClipboardEntry::new("content1".to_string(), None, None);
+        let entry2 = ClipboardEntry::new("content2".to_string(), None, None);
+
+        assert_ne!(entry1.id, entry2.id);
+    }
+
+    #[test]
+    fn test_clipboard_entry_serialization() {
+        let entry = ClipboardEntry::new(
+            "fn main() {}".to_string(),
+            Some("rust".to_string()),
+            Some("lib.rs".to_string()),
+        );
+
+        let json = serde_json::to_string(&entry).unwrap();
+        assert!(json.contains("fn main() {}"));
+        assert!(json.contains("rust"));
+        assert!(json.contains("lib.rs"));
+        assert!(json.contains("is_pinned"));
+
+        let deserialized: ClipboardEntry = serde_json::from_str(&json).unwrap();
+        assert_eq!(deserialized.content, entry.content);
+        assert_eq!(deserialized.language, entry.language);
+        assert_eq!(deserialized.source, entry.source);
+        assert_eq!(deserialized.id, entry.id);
+    }
+
+    #[test]
+    fn test_clipboard_entry_clone() {
+        let entry = ClipboardEntry::new(
+            "original".to_string(),
+            Some("python".to_string()),
+            None,
+        );
+
+        let cloned = entry.clone();
+        assert_eq!(cloned.content, entry.content);
+        assert_eq!(cloned.id, entry.id);
+        assert_eq!(cloned.language, entry.language);
+    }
+
+    #[test]
+    fn test_clipboard_entry_timestamp_is_rfc3339() {
+        let entry = ClipboardEntry::new("test".to_string(), None, None);
+
+        // RFC3339 timestamp should parse successfully
+        let parsed = chrono::DateTime::parse_from_rfc3339(&entry.timestamp);
+        assert!(parsed.is_ok());
+    }
+
+    // ==================== ClipboardHistory tests ====================
+
+    #[test]
+    fn test_clipboard_history_default() {
+        let history = ClipboardHistory::default();
+        assert!(history.entries.is_empty());
+    }
+
+    #[test]
+    fn test_clipboard_history_serialization() {
+        let mut history = ClipboardHistory::default();
+        history.entries.push(ClipboardEntry::new(
+            "entry1".to_string(),
+            Some("js".to_string()),
+            None,
+        ));
+        history.entries.push(ClipboardEntry::new(
+            "entry2".to_string(),
+            None,
+            Some("file.txt".to_string()),
+        ));
+
+        let json = serde_json::to_string(&history).unwrap();
+        assert!(json.contains("entry1"));
+        assert!(json.contains("entry2"));
+        assert!(json.contains("js"));
+        assert!(json.contains("file.txt"));
+
+        let deserialized: ClipboardHistory = serde_json::from_str(&json).unwrap();
+        assert_eq!(deserialized.entries.len(), 2);
+    }
+
+    #[test]
+    fn test_clipboard_history_entries_order() {
+        let mut history = ClipboardHistory::default();
+
+        history.entries.push(ClipboardEntry::new("first".to_string(), None, None));
+        history.entries.push(ClipboardEntry::new("second".to_string(), None, None));
+        history.entries.push(ClipboardEntry::new("third".to_string(), None, None));
+
+        assert_eq!(history.entries[0].content, "first");
+        assert_eq!(history.entries[1].content, "second");
+        assert_eq!(history.entries[2].content, "third");
+    }
+
+    // ==================== ClipboardState tests ====================
+
+    #[test]
+    fn test_clipboard_state_default() {
+        let state = ClipboardState::default();
+        assert!(state.last_content.is_none());
+    }
+
+    #[test]
+    fn test_clipboard_state_with_content() {
+        let state = ClipboardState {
+            last_content: Some("cached content".to_string()),
+        };
+        assert_eq!(state.last_content, Some("cached content".to_string()));
+    }
+
+    // ==================== MAX_HISTORY_SIZE constant test ====================
+
+    #[test]
+    fn test_max_history_size_is_reasonable() {
+        assert_eq!(MAX_HISTORY_SIZE, 100);
+        // Compile-time assertions for constant bounds
+        const _: () = assert!(MAX_HISTORY_SIZE > 0);
+        const _: () = assert!(MAX_HISTORY_SIZE <= 1000); // Sanity check
+    }
+
+    // ==================== Pinned entry sorting tests ====================
+
+    #[test]
+    #[allow(clippy::useless_vec)]
+    fn test_pinned_entries_sorting() {
+        let mut entries = vec![
+            ClipboardEntry {
+                id: "1".to_string(),
+                content: "unpinned older".to_string(),
+                language: None,
+                source: None,
+                timestamp: "2024-01-01T00:00:00Z".to_string(),
+                is_pinned: false,
+            },
+            ClipboardEntry {
+                id: "2".to_string(),
+                content: "pinned".to_string(),
+                language: None,
+                source: None,
+                timestamp: "2024-01-02T00:00:00Z".to_string(),
+                is_pinned: true,
+            },
+            ClipboardEntry {
+                id: "3".to_string(),
+                content: "unpinned newer".to_string(),
+                language: None,
+                source: None,
+                timestamp: "2024-01-03T00:00:00Z".to_string(),
+                is_pinned: false,
+            },
+        ];
+
+        // Apply the same sorting logic as used in the module
+        entries.sort_by(|a, b| {
+            if a.is_pinned && !b.is_pinned {
+                std::cmp::Ordering::Less
+            } else if !a.is_pinned && b.is_pinned {
+                std::cmp::Ordering::Greater
+            } else {
+                b.timestamp.cmp(&a.timestamp)
+            }
+        });
+
+        // Pinned should be first
+        assert!(entries[0].is_pinned);
+        assert_eq!(entries[0].id, "2");
+
+        // Then unpinned sorted by timestamp descending (newest first)
+        assert_eq!(entries[1].id, "3"); // newer unpinned
+        assert_eq!(entries[2].id, "1"); // older unpinned
+    }
+
+    #[test]
+    #[allow(clippy::useless_vec)]
+    fn test_multiple_pinned_entries_sorting() {
+        let mut entries = vec![
+            ClipboardEntry {
+                id: "1".to_string(),
+                content: "pinned older".to_string(),
+                language: None,
+                source: None,
+                timestamp: "2024-01-01T00:00:00Z".to_string(),
+                is_pinned: true,
+            },
+            ClipboardEntry {
+                id: "2".to_string(),
+                content: "unpinned".to_string(),
+                language: None,
+                source: None,
+                timestamp: "2024-01-02T00:00:00Z".to_string(),
+                is_pinned: false,
+            },
+            ClipboardEntry {
+                id: "3".to_string(),
+                content: "pinned newer".to_string(),
+                language: None,
+                source: None,
+                timestamp: "2024-01-03T00:00:00Z".to_string(),
+                is_pinned: true,
+            },
+        ];
+
+        entries.sort_by(|a, b| {
+            if a.is_pinned && !b.is_pinned {
+                std::cmp::Ordering::Less
+            } else if !a.is_pinned && b.is_pinned {
+                std::cmp::Ordering::Greater
+            } else {
+                b.timestamp.cmp(&a.timestamp)
+            }
+        });
+
+        // Both pinned first, sorted by timestamp
+        assert!(entries[0].is_pinned);
+        assert_eq!(entries[0].id, "3"); // pinned newer
+        assert!(entries[1].is_pinned);
+        assert_eq!(entries[1].id, "1"); // pinned older
+        // Then unpinned
+        assert!(!entries[2].is_pinned);
+        assert_eq!(entries[2].id, "2");
+    }
+
+    // ==================== Entry filtering tests ====================
+
+    #[test]
+    fn test_filter_entries_by_language() {
+        let history = ClipboardHistory {
+            entries: vec![
+                ClipboardEntry {
+                    id: "1".to_string(),
+                    content: "rust code".to_string(),
+                    language: Some("rust".to_string()),
+                    source: None,
+                    timestamp: "2024-01-01T00:00:00Z".to_string(),
+                    is_pinned: false,
+                },
+                ClipboardEntry {
+                    id: "2".to_string(),
+                    content: "js code".to_string(),
+                    language: Some("javascript".to_string()),
+                    source: None,
+                    timestamp: "2024-01-02T00:00:00Z".to_string(),
+                    is_pinned: false,
+                },
+                ClipboardEntry {
+                    id: "3".to_string(),
+                    content: "more rust".to_string(),
+                    language: Some("rust".to_string()),
+                    source: None,
+                    timestamp: "2024-01-03T00:00:00Z".to_string(),
+                    is_pinned: false,
+                },
+            ],
+        };
+
+        let filtered: Vec<_> = history
+            .entries
+            .iter()
+            .filter(|e| e.language.as_ref() == Some(&"rust".to_string()))
+            .collect();
+
+        assert_eq!(filtered.len(), 2);
+        assert!(filtered.iter().all(|e| e.language == Some("rust".to_string())));
+    }
+
+    #[test]
+    fn test_search_entries_by_content() {
+        let history = ClipboardHistory {
+            entries: vec![
+                ClipboardEntry {
+                    id: "1".to_string(),
+                    content: "fn hello_world()".to_string(),
+                    language: Some("rust".to_string()),
+                    source: None,
+                    timestamp: "2024-01-01T00:00:00Z".to_string(),
+                    is_pinned: false,
+                },
+                ClipboardEntry {
+                    id: "2".to_string(),
+                    content: "function hello()".to_string(),
+                    language: Some("javascript".to_string()),
+                    source: None,
+                    timestamp: "2024-01-02T00:00:00Z".to_string(),
+                    is_pinned: false,
+                },
+                ClipboardEntry {
+                    id: "3".to_string(),
+                    content: "def goodbye()".to_string(),
+                    language: Some("python".to_string()),
+                    source: None,
+                    timestamp: "2024-01-03T00:00:00Z".to_string(),
+                    is_pinned: false,
+                },
+            ],
+        };
+
+        let query = "hello";
+        let query_lower = query.to_lowercase();
+        let filtered: Vec<_> = history
+            .entries
+            .iter()
+            .filter(|e| e.content.to_lowercase().contains(&query_lower))
+            .collect();
+
+        assert_eq!(filtered.len(), 2);
+        assert!(filtered[0].content.contains("hello"));
+        assert!(filtered[1].content.contains("hello"));
+    }
+
+    #[test]
+    fn test_search_entries_case_insensitive() {
+        let history = ClipboardHistory {
+            entries: vec![
+                ClipboardEntry {
+                    id: "1".to_string(),
+                    content: "HELLO WORLD".to_string(),
+                    language: None,
+                    source: None,
+                    timestamp: "2024-01-01T00:00:00Z".to_string(),
+                    is_pinned: false,
+                },
+            ],
+        };
+
+        let query = "hello";
+        let query_lower = query.to_lowercase();
+        let filtered: Vec<_> = history
+            .entries
+            .iter()
+            .filter(|e| e.content.to_lowercase().contains(&query_lower))
+            .collect();
+
+        assert_eq!(filtered.len(), 1);
+    }
+
+    // ==================== Unique languages extraction test ====================
+
+    #[test]
+    fn test_extract_unique_languages() {
+        let history = ClipboardHistory {
+            entries: vec![
+                ClipboardEntry {
+                    id: "1".to_string(),
+                    content: "".to_string(),
+                    language: Some("rust".to_string()),
+                    source: None,
+                    timestamp: "".to_string(),
+                    is_pinned: false,
+                },
+                ClipboardEntry {
+                    id: "2".to_string(),
+                    content: "".to_string(),
+                    language: Some("javascript".to_string()),
+                    source: None,
+                    timestamp: "".to_string(),
+                    is_pinned: false,
+                },
+                ClipboardEntry {
+                    id: "3".to_string(),
+                    content: "".to_string(),
+                    language: Some("rust".to_string()), // Duplicate
+                    source: None,
+                    timestamp: "".to_string(),
+                    is_pinned: false,
+                },
+                ClipboardEntry {
+                    id: "4".to_string(),
+                    content: "".to_string(),
+                    language: None, // No language
+                    source: None,
+                    timestamp: "".to_string(),
+                    is_pinned: false,
+                },
+            ],
+        };
+
+        let mut languages: Vec<String> = history
+            .entries
+            .iter()
+            .filter_map(|e| e.language.clone())
+            .collect();
+        languages.sort();
+        languages.dedup();
+
+        assert_eq!(languages.len(), 2);
+        assert!(languages.contains(&"rust".to_string()));
+        assert!(languages.contains(&"javascript".to_string()));
+    }
+
+    // ==================== Retain pinned entries test ====================
+
+    #[test]
+    fn test_retain_pinned_on_clear() {
+        let mut history = ClipboardHistory {
+            entries: vec![
+                ClipboardEntry {
+                    id: "1".to_string(),
+                    content: "pinned".to_string(),
+                    language: None,
+                    source: None,
+                    timestamp: "".to_string(),
+                    is_pinned: true,
+                },
+                ClipboardEntry {
+                    id: "2".to_string(),
+                    content: "unpinned".to_string(),
+                    language: None,
+                    source: None,
+                    timestamp: "".to_string(),
+                    is_pinned: false,
+                },
+                ClipboardEntry {
+                    id: "3".to_string(),
+                    content: "another pinned".to_string(),
+                    language: None,
+                    source: None,
+                    timestamp: "".to_string(),
+                    is_pinned: true,
+                },
+            ],
+        };
+
+        // Simulate clear (keep only pinned)
+        history.entries.retain(|e| e.is_pinned);
+
+        assert_eq!(history.entries.len(), 2);
+        assert!(history.entries.iter().all(|e| e.is_pinned));
+    }
+}