add week 1 day 2 tutorial

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm/src/tests/harness.rs

@@ -0,0 +1,70 @@
+use anyhow::{bail, Result};
+use bytes::Bytes;
+
+use crate::iterators::StorageIterator;
+
+#[derive(Clone)]
+pub struct MockIterator {
+    pub data: Vec<(Bytes, Bytes)>,
+    pub error_when: Option<usize>,
+    pub index: usize,
+}
+
+impl MockIterator {
+    pub fn new(data: Vec<(Bytes, Bytes)>) -> Self {
+        Self {
+            data,
+            index: 0,
+            error_when: None,
+        }
+    }
+
+    pub fn new_with_error(data: Vec<(Bytes, Bytes)>, error_when: usize) -> Self {
+        Self {
+            data,
+            index: 0,
+            error_when: Some(error_when),
+        }
+    }
+}
+
+impl StorageIterator for MockIterator {
+    fn next(&mut self) -> Result<()> {
+        if self.index < self.data.len() {
+            self.index += 1;
+        }
+        if let Some(error_when) = self.error_when {
+            if self.index == error_when {
+                bail!("fake error!");
+            }
+        }
+        Ok(())
+    }
+
+    fn key(&self) -> &[u8] {
+        if let Some(error_when) = self.error_when {
+            if self.index >= error_when {
+                panic!("invalid access after next returns an error!");
+            }
+        }
+        self.data[self.index].0.as_ref()
+    }
+
+    fn value(&self) -> &[u8] {
+        if let Some(error_when) = self.error_when {
+            if self.index >= error_when {
+                panic!("invalid access after next returns an error!");
+            }
+        }
+        self.data[self.index].1.as_ref()
+    }
+
+    fn is_valid(&self) -> bool {
+        if let Some(error_when) = self.error_when {
+            if self.index >= error_when {
+                panic!("invalid access after next returns an error!");
+            }
+        }
+        self.index < self.data.len()
+    }
+}