1 files changed, 51 insertions, 0 deletions
diff --git a/packages/lsp/src/diagnostics.test.ts b/packages/lsp/src/diagnostics.test.ts
new file mode 100644
index 0000000..9f2b6b4
--- /dev/null
+++ b/packages/lsp/src/diagnostics.test.ts
@@ -0,0 +1,51 @@
+import { describe, expect, it } from "vitest";
+import { DiagnosticsStore } from "./diagnostics.js";
+
+describe("diagnostics", () => {
+	it("formats diagnostics with severity, location, and message", () => {
+		const store = new DiagnosticsStore();
+		store.setPushDiagnostics({
+			uri: "file:///test.ts",
+			diagnostics: [
+				{
+					range: { start: { line: 0, character: 5 }, end: { line: 0, character: 10 } },
+					severity: 1,
+					source: "typescript",
+					message: "Cannot find name 'hello'.",
+				},
+			],
+		});
+
+		const formatted = store.format("file:///test.ts");
+		expect(formatted).toContain("ERROR");
+		expect(formatted).toContain("L1:6");
+		expect(formatted).toContain("Cannot find name 'hello'.");
+		expect(formatted).toContain("[typescript]");
+	});
+
+	it("merges push and pull diagnostics with deduplication", () => {
+		const store = new DiagnosticsStore();
+		const diag = {
+			range: { start: { line: 0, character: 0 }, end: { line: 0, character: 5 } },
+			severity: 1,
+			message: "Error",
+		};
+
+		store.setPushDiagnostics({
+			uri: "file:///test.ts",
+			diagnostics: [diag],
+		});
+		store.setPullDiagnostics("file:///test.ts", {
+			kind: "full",
+			items: [diag],
+		});
+
+		const merged = store.getMerged("file:///test.ts");
+		expect(merged).toHaveLength(1);
+	});
+
+	it("returns empty string when no diagnostics exist", () => {
+		const store = new DiagnosticsStore();
+		expect(store.format("file:///nonexistent.ts")).toBe("");
+	});
+});