1 files changed, 73 insertions, 1 deletions
diff --git a/src/utils/datetime.test.ts b/src/utils/datetime.test.ts
index 5f0749d..03e2771 100644
--- a/src/utils/datetime.test.ts
+++ b/src/utils/datetime.test.ts
@@ -1,6 +1,10 @@
 import { assertEquals, assertMatch } from "@std/assert";
 import { describe, it } from "@std/testing/bdd";
-import { toIso8601Full, toIso8601FullUTC } from "./datetime.ts";
+import {
+  getRelativeTimeUnit,
+  toIso8601Full,
+  toIso8601FullUTC,
+} from "./datetime.ts";
 
 describe("toIso8601Full", () => {
   it("formats current local time with offset", () => {
@@ -60,3 +64,71 @@ describe("toIso8601FullUTC", () => {
     assertMatch(result, /^-\d{6}-03-15T12:00:00\.000Z$/);
   });
 });
+
+describe("getRelativeTimeUnit", () => {
+  const now = new Date();
+
+  it("returns seconds for differences under a minute", () => {
+    const future = new Date(now.getTime() + 45 * 1000);
+    const [value, unit] = getRelativeTimeUnit(future);
+
+    assertEquals(unit, "second");
+    assertEquals(value, 1);
+  });
+
+  it("returns minutes for differences under an hour but over a minute", () => {
+    const future = new Date(now.getTime() + 15 * 60 * 1000);
+    const [value, unit] = getRelativeTimeUnit(future);
+
+    assertEquals(unit, "minute");
+    assertEquals(value, 15);
+  });
+
+  it("returns hours for differences under a day but over an hour", () => {
+    const past = new Date(now.getTime() - 3.2 * 60 * 60 * 1000);
+    const [value, unit] = getRelativeTimeUnit(past);
+
+    assertEquals(unit, "hour");
+    assertEquals(value, -3);
+  });
+
+  it("returns days for differences under a week but over a day", () => {
+    const past = new Date(now.getTime() - 2.5 * 24 * 60 * 60 * 1000);
+    const [value, unit] = getRelativeTimeUnit(past);
+
+    assertEquals(unit, "day");
+    assertEquals(value, -3);
+  });
+
+  it("returns weeks for differences under a month but over a week", () => {
+    const future = new Date(now.getTime() + 2.3 * 7 * 24 * 60 * 60 * 1000);
+    const [value, unit] = getRelativeTimeUnit(future);
+
+    assertEquals(unit, "week");
+    assertEquals(value, 2);
+  });
+
+  it("returns months for differences under a quarter but over a month", () => {
+    const past = new Date(now.getTime() - 1.5 * 30 * 24 * 60 * 60 * 1000);
+    const [value, unit] = getRelativeTimeUnit(past);
+
+    assertEquals(unit, "month");
+    assertEquals(value, -2);
+  });
+
+  it("returns quarters for differences under a year but over a quarter", () => {
+    const future = new Date(now.getTime() + 5 * 30 * 24 * 60 * 60 * 1000);
+    const [value, unit] = getRelativeTimeUnit(future);
+
+    assertEquals(unit, "quarter");
+    assertEquals(value, 2);
+  });
+
+  it("returns years for differences over a year", () => {
+    const past = new Date(now.getTime() - 3.4 * 365 * 24 * 60 * 60 * 1000);
+    const [value, unit] = getRelativeTimeUnit(past);
+
+    assertEquals(unit, "year");
+    assertEquals(value, -3);
+  });
+});