diff --git a/TEST_README.md b/TEST_README.md
new file mode 100644
index 0000000..8dfc635
--- /dev/null
+++ b/TEST_README.md
@@ -0,0 +1,61 @@
+# Tests for findClosestRationalAngle
+
+This directory contains comprehensive tests for the `findClosestRationalAngle` function.
+
+## Running the Tests
+
+To run all tests:
+```bash
+deno test --allow-read
+```
+
+Or using the task defined in `deno.json`:
+```bash
+deno task test
+```
+
+To run just the lib tests:
+```bash
+deno test src/lib_test.ts --allow-read
+```
+
+## Test Coverage
+
+The test suite for `findClosestRationalAngle` covers:
+
+### Exact Matches
+- Tests for angles that exactly match rational angles in the RATIONAL_ANGLES array
+- Examples: 0°, 45°, 90°, -45°, -90°, 26.565°
+
+### Closest Angle Finding
+- Tests for angles that are close to but not exactly matching rational angles
+- Examples: 44° → 45°, 46° → 45°, 25° → 26.565°, 30° → 26.565°
+
+### Angle Normalization
+- Tests for angles > 360° (e.g., 405° → 45°, 720° → 0°)
+- Tests for negative angles (e.g., -45°, -90°, -30°)
+- Tests for very large angles (e.g., 1440°, -1440°)
+- Tests for edge cases around 0° (e.g., 359°, 1°, -1°, -359°)
+
+### Fractional Angles
+- Tests for non-integer angles (e.g., 44.5° → 45°)
+
+### Edge Cases
+- Tests for angles near boundaries (e.g., 89° → 90°, 91° → 90°)
+- Tests that verify the result always comes from RATIONAL_ANGLES array
+- Tests that verify all required fields are present in the returned angleEntry object
+
+## Test Count
+
+The test suite includes **27 comprehensive test cases** covering all aspects of the `findClosestRationalAngle` function.
+
+## Function Behavior
+
+The `findClosestRationalAngle` function:
+1. Normalizes input angles to the 0-360° range
+2. Finds the rational angle with the smallest absolute difference from the normalized angle
+3. Returns an `angleEntry` object containing:
+   - `degrees`: The angle in degrees
+   - `m`: The numerator of the rational angle (tan(θ) = m/n)
+   - `n`: The denominator of the rational angle (tan(θ) = m/n)
+   - `label`: A human-readable label for the angle
diff --git a/deno.json b/deno.json
index b61140f..2d64b1b 100644
--- a/deno.json
+++ b/deno.json
@@ -6,7 +6,8 @@
     "sharp": "npm:sharp@^0.34.5"
   },
   "tasks": {
-    "compile": "deno compile --allow-all main.ts"
+    "compile": "deno compile --allow-all main.ts",
+    "test": "deno test --allow-read"
   },
   "version": "0.0.1"
 }
diff --git a/src/lib_test.ts b/src/lib_test.ts
new file mode 100644
index 0000000..963b9ed
--- /dev/null
+++ b/src/lib_test.ts
@@ -0,0 +1,190 @@
+import { findClosestRationalAngle, RATIONAL_ANGLES, type angleEntry } from "./lib.ts";
+
+Deno.test("findClosestRationalAngle - exact match for 0 degrees", () => {
+  const result = findClosestRationalAngle(0);
+  if (result.degrees !== 0) throw new Error(`Expected 0, got ${result.degrees}`);
+  if (result.m !== 0) throw new Error(`Expected m=0, got ${result.m}`);
+  if (result.n !== 1) throw new Error(`Expected n=1, got ${result.n}`);
+  if (result.label !== "0°") throw new Error(`Expected label "0°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - exact match for 45 degrees", () => {
+  const result = findClosestRationalAngle(45);
+  if (result.degrees !== 45) throw new Error(`Expected 45, got ${result.degrees}`);
+  if (result.m !== 1) throw new Error(`Expected m=1, got ${result.m}`);
+  if (result.n !== 1) throw new Error(`Expected n=1, got ${result.n}`);
+  if (result.label !== "45°") throw new Error(`Expected label "45°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - exact match for 90 degrees", () => {
+  const result = findClosestRationalAngle(90);
+  if (result.degrees !== 90) throw new Error(`Expected 90, got ${result.degrees}`);
+  if (result.m !== 1) throw new Error(`Expected m=1, got ${result.m}`);
+  if (result.n !== 0) throw new Error(`Expected n=0, got ${result.n}`);
+  if (result.label !== "90°") throw new Error(`Expected label "90°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - exact match for -45 degrees", () => {
+  const result = findClosestRationalAngle(-45);
+  if (result.degrees !== -45) throw new Error(`Expected -45, got ${result.degrees}`);
+  if (result.m !== -1) throw new Error(`Expected m=-1, got ${result.m}`);
+  if (result.n !== 1) throw new Error(`Expected n=1, got ${result.n}`);
+  if (result.label !== "-45°") throw new Error(`Expected label "-45°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - exact match for -90 degrees", () => {
+  const result = findClosestRationalAngle(-90);
+  if (result.degrees !== -90) throw new Error(`Expected -90, got ${result.degrees}`);
+  if (result.m !== -1) throw new Error(`Expected m=-1, got ${result.m}`);
+  if (result.n !== 0) throw new Error(`Expected n=0, got ${result.n}`);
+  if (result.label !== "-90°") throw new Error(`Expected label "-90°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - exact match for 26.565 degrees", () => {
+  const result = findClosestRationalAngle(26.565);
+  if (result.degrees !== 26.565) throw new Error(`Expected 26.565, got ${result.degrees}`);
+  if (result.m !== 1) throw new Error(`Expected m=1, got ${result.m}`);
+  if (result.n !== 2) throw new Error(`Expected n=2, got ${result.n}`);
+  if (result.label !== "26.565° (arctan 1/2)") throw new Error(`Expected label "26.565° (arctan 1/2)", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - finds closest angle for 44 degrees", () => {
+  const result = findClosestRationalAngle(44);
+  if (result.degrees !== 45) throw new Error(`Expected 45, got ${result.degrees}`);
+  if (result.label !== "45°") throw new Error(`Expected label "45°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - finds closest angle for 46 degrees", () => {
+  const result = findClosestRationalAngle(46);
+  if (result.degrees !== 45) throw new Error(`Expected 45, got ${result.degrees}`);
+  if (result.label !== "45°") throw new Error(`Expected label "45°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - finds closest angle for 25 degrees", () => {
+  const result = findClosestRationalAngle(25);
+  if (result.degrees !== 26.565) throw new Error(`Expected 26.565, got ${result.degrees}`);
+  if (result.label !== "26.565° (arctan 1/2)") throw new Error(`Expected label "26.565° (arctan 1/2)", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - finds closest angle for 30 degrees", () => {
+  const result = findClosestRationalAngle(30);
+  // 30 is closer to 26.565 (diff: 3.435) than to 33.69 (diff: 3.69)
+  if (result.degrees !== 26.565) throw new Error(`Expected 26.565, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles angle > 360 degrees (405)", () => {
+  const result = findClosestRationalAngle(405);
+  // 405 % 360 = 45
+  if (result.degrees !== 45) throw new Error(`Expected 45, got ${result.degrees}`);
+  if (result.label !== "45°") throw new Error(`Expected label "45°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - handles angle > 360 degrees (370)", () => {
+  const result = findClosestRationalAngle(370);
+  // 370 % 360 = 10, closest to 11.31° (arctan 1/5)
+  if (result.degrees !== 11.31) throw new Error(`Expected 11.31, got ${result.degrees}`);
+  if (result.label !== "11.310° (arctan 1/5)") throw new Error(`Expected label "11.310° (arctan 1/5)", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - handles large positive angle (720)", () => {
+  const result = findClosestRationalAngle(720);
+  // 720 % 360 = 0
+  if (result.degrees !== 0) throw new Error(`Expected 0, got ${result.degrees}`);
+  if (result.label !== "0°") throw new Error(`Expected label "0°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - handles negative angle (-45)", () => {
+  const result = findClosestRationalAngle(-45);
+  if (result.degrees !== -45) throw new Error(`Expected -45, got ${result.degrees}`);
+  if (result.label !== "-45°") throw new Error(`Expected label "-45°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - handles negative angle (-90)", () => {
+  const result = findClosestRationalAngle(-90);
+  if (result.degrees !== -90) throw new Error(`Expected -90, got ${result.degrees}`);
+  if (result.label !== "-90°") throw new Error(`Expected label "-90°", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - handles negative angle (-30)", () => {
+  const result = findClosestRationalAngle(-30);
+  // -30 % 360 = -30, then +360 = 330
+  // 330 is closest to -26.565° (which normalizes to 333.435°, diff: 3.435)
+  if (result.degrees !== -26.565) throw new Error(`Expected -26.565, got ${result.degrees}`);
+  if (result.label !== "-26.565° (arctan -1/2)") throw new Error(`Expected "-26.565° (arctan -1/2)", got ${result.label}`);
+});
+
+Deno.test("findClosestRationalAngle - handles angle close to 0 from negative side (-1)", () => {
+  const result = findClosestRationalAngle(-1);
+  // -1 % 360 = -1, then +360 = 359, closest to 0°
+  if (result.degrees !== 0) throw new Error(`Expected 0, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles angle 359 degrees", () => {
+  const result = findClosestRationalAngle(359);
+  // 359 is closest to 0° (1 degree away)
+  if (result.degrees !== 0) throw new Error(`Expected 0, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles angle 1 degree", () => {
+  const result = findClosestRationalAngle(1);
+  // 1 is closest to 0°
+  if (result.degrees !== 0) throw new Error(`Expected 0, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles negative angle close to -360 (-359)", () => {
+  const result = findClosestRationalAngle(-359);
+  // -359 % 360 = -359, then +360 = 1, closest to 0°
+  if (result.degrees !== 0) throw new Error(`Expected 0, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles very large positive angle (1440)", () => {
+  const result = findClosestRationalAngle(1440); // 4 full rotations
+  // 1440 % 360 = 0
+  if (result.degrees !== 0) throw new Error(`Expected 0, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles very large negative angle (-1440)", () => {
+  const result = findClosestRationalAngle(-1440); // -4 full rotations
+  // -1440 % 360 = 0
+  if (result.degrees !== 0) throw new Error(`Expected 0, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles fractional angle 44.5", () => {
+  const result = findClosestRationalAngle(44.5);
+  // 44.5 is closest to 45° (0.5 away)
+  if (result.degrees !== 45) throw new Error(`Expected 45, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles angle 89", () => {
+  const result = findClosestRationalAngle(89);
+  // 89 is closest to 90° (1 away) vs 78.69° (10.31 away)
+  if (result.degrees !== 90) throw new Error(`Expected 90, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - handles angle 91", () => {
+  const result = findClosestRationalAngle(91);
+  // 91 is closest to 90° (1 away)
+  if (result.degrees !== 90) throw new Error(`Expected 90, got ${result.degrees}`);
+});
+
+Deno.test("findClosestRationalAngle - returns an angleEntry object with all required fields", () => {
+  const result = findClosestRationalAngle(45);
+  if (typeof result.degrees !== "number") throw new Error("degrees should be number");
+  if (typeof result.m !== "number") throw new Error("m should be number");
+  if (typeof result.n !== "number") throw new Error("n should be number");
+  if (typeof result.label !== "string") throw new Error("label should be string");
+});
+
+Deno.test("findClosestRationalAngle - always returns one of the predefined RATIONAL_ANGLES", () => {
+  const testAngles = [0, 15, 30, 45, 60, 75, 90, 180, 270, -45, -90, 360, 400];
+  
+  for (const angle of testAngles) {
+    const result = findClosestRationalAngle(angle);
+    const isInArray = RATIONAL_ANGLES.some(
+      (ra) => ra.degrees === result.degrees && ra.label === result.label
+    );
+    if (!isInArray) {
+      throw new Error(`Result for angle ${angle} should be in RATIONAL_ANGLES`);
+    }
+  }
+});