Add deterministic-tests (#190)

Reviewed-on: https://home.schmelczer.dev/git/git/andras/vault-link/pulls/190
Co-authored-by: Andras Schmelczer <andras@schmelczer.dev>
Co-committed-by: Andras Schmelczer <andras@schmelczer.dev>

frontend/deterministic-tests/src/tests/coalesce-update-remote-update-data-loss.test.ts

@@ -0,0 +1,59 @@
+import type { AssertableState } from "../utils/assertable-state";
+import type { TestDefinition } from "../test-definition";
+
+export const coalesceUpdateRemoteUpdateDataLossTest: TestDefinition = {
+    description:
+        "Divergent offline edits with text-merge expectation. Client 0's " +
+        "remote update fully lands before Client 1 reconnects (`sync`-after " +
+        "the c0 update enforces this), so Client 1's offline edit merges " +
+        "against a server-known version, not a coalesced batch. Both " +
+        "additions must survive in the final merged content. (Filename's " +
+        "'coalesce' framing is aspirational — a true update-coalesce test " +
+        "would skip the c0 sync and queue overlapping local + remote " +
+        "updates against the same parent version.)",
+    clients: 2,
+    steps: [
+        {
+            type: "create",
+            client: 0,
+            path: "doc.md",
+            content: "line 1\nline 2\nline 3"
+        },
+        { type: "enable-sync", client: 0 },
+        { type: "enable-sync", client: 1 },
+        { type: "barrier" },
+
+        { type: "disable-sync", client: 1 },
+
+        {
+            type: "update",
+            client: 0,
+            path: "doc.md",
+            content: "line 1\nline 2\nline 3\nclient 0 addition"
+        },
+        { type: "sync", client: 0 },
+
+        {
+            type: "update",
+            client: 1,
+            path: "doc.md",
+            content: "client 1 addition\nline 1\nline 2\nline 3"
+        },
+
+        { type: "enable-sync", client: 1 },
+        { type: "barrier" },
+
+        {
+            type: "assert-consistent",
+            verify: (state: AssertableState): void => {
+                state
+                    .assertFileCount(1)
+                    .assertContains(
+                        "doc.md",
+                        "client 0 addition",
+                        "client 1 addition"
+                    );
+            }
+        }
+    ]
+};