Commit LLM generated test cases

frontend/deterministic-tests/src/tests/concurrent-edit-exact-same-position.test.ts

@@ -0,0 +1,91 @@
+import type { ClientState, TestDefinition } from "../test-definition";
+import { assert } from "../utils/assert";
+
+function verifyMergedEdits(state: ClientState): void {
+    assert(
+        state.files.size === 1,
+        `Expected 1 file, got ${state.files.size}`
+    );
+    assert(
+        state.files.has("doc.md"),
+        `Expected doc.md to exist`
+    );
+    const content = state.files.get("doc.md") ?? "";
+
+    // Both clients replaced the same word. The 3-way merge with
+    // parent "the quick brown fox" should detect that both sides
+    // changed "quick" — one to "slow" and one to "fast".
+    // reconcile-text does word-level tokenization, so both
+    // replacements should appear (though order may vary).
+    assert(
+        content.includes("slow") && content.includes("fast"),
+        `Expected merged content to contain both "slow" and "fast", got: "${content}"`
+    );
+    assert(
+        content.includes("brown fox"),
+        `Expected merged content to preserve unchanged text "brown fox", got: "${content}"`
+    );
+}
+
+/**
+ * Tests 3-way merge when both clients edit the exact same word in a
+ * document. Client 0 replaces "quick" with "slow", Client 1 replaces
+ * "quick" with "fast". The merge should detect the conflicting edits
+ * and preserve both (the merge algorithm does not silently drop one).
+ *
+ * This is a stress test for the reconcile-text library's word-level
+ * tokenizer when operating on overlapping changes at the same offset.
+ */
+export const concurrentEditExactSamePositionTest: TestDefinition = {
+    name: "Concurrent Edit at Exact Same Position",
+    description:
+        "Both clients edit the exact same word in a file. Client 0 changes " +
+        "'quick' to 'slow', Client 1 changes 'quick' to 'fast'. The 3-way " +
+        "merge should detect the overlapping edit and produce a result that " +
+        "preserves both changes.",
+    clients: 2,
+    steps: [
+        // Setup: shared document
+        {
+            type: "create",
+            client: 0,
+            path: "doc.md",
+            content: "the quick brown fox"
+        },
+        { type: "enable-sync", client: 0 },
+        { type: "enable-sync", client: 1 },
+        { type: "sync" },
+        { type: "barrier" },
+        {
+            type: "assert-content",
+            client: 1,
+            path: "doc.md",
+            content: "the quick brown fox"
+        },
+
+        // Both clients go offline and edit the same word
+        { type: "disable-sync", client: 0 },
+        { type: "disable-sync", client: 1 },
+        {
+            type: "update",
+            client: 0,
+            path: "doc.md",
+            content: "the slow brown fox"
+        },
+        {
+            type: "update",
+            client: 1,
+            path: "doc.md",
+            content: "the fast brown fox"
+        },
+
+        // Both come online
+        { type: "enable-sync", client: 0 },
+        { type: "enable-sync", client: 1 },
+        { type: "sync" },
+        { type: "barrier" },
+
+        // Both should converge to a merged result
+        { type: "assert-consistent", verify: verifyMergedEdits }
+    ]
+};