diff --git a/ProgressOfTesting.txt b/ProgressOfTesting.txt
index 9387d85..5c34b22 100644
--- a/ProgressOfTesting.txt
+++ b/ProgressOfTesting.txt
@@ -1,6 +1,6 @@
 [ ] 未开始测试 - 25 (35.71%)
-[-] 测试未完成 - 13 (18.57%)
-[Y] 测试完成 - 20 (28.57%)
+[-] 测试未完成 - 12 (17.14%)
+[Y] 测试完成 - 21 (30.00%)
 [x] 无需测试 - 12 (17.14%)
 
 xyz.zhouxy.plusone.commons
@@ -79,7 +79,7 @@ xyz.zhouxy.plusone.commons
     │       SQL.java                              [ ]
     │
     ├───time
-    │       Quarter.java                          [-]
+    │       Quarter.java                          [Y]
     │       YearQuarter.java                      [-]
     │
     └───util
diff --git a/src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java b/src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java
index cbc38e1..71efd48 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java
@@ -116,12 +116,12 @@ public enum Quarter implements IWithIntCode {
 
     // computes
 
-    public Quarter plus(long quarters) { // TODO 单元测试
+    public Quarter plus(long quarters) {
         final int amount = (int) ((quarters % 4) + 4);
         return ENUMS[(ordinal() + amount) % 4];
     }
 
-    public Quarter minus(long quarters) { // TODO 单元测试
+    public Quarter minus(long quarters) {
         return plus(-(quarters % 4));
     }
 
diff --git a/src/test/java/xyz/zhouxy/plusone/commons/time/QuarterTests.java b/src/test/java/xyz/zhouxy/plusone/commons/time/QuarterTests.java
index 69637a8..75f583f 100644
--- a/src/test/java/xyz/zhouxy/plusone/commons/time/QuarterTests.java
+++ b/src/test/java/xyz/zhouxy/plusone/commons/time/QuarterTests.java
@@ -240,4 +240,116 @@ class QuarterTests {
         firstDayOfYear = Quarter.Q4.firstDayOfYear(false);
         assertEquals(1 + (31 + 28 + 31) + (30 + 31 + 30) + (31 + 30 + 31), firstDayOfYear);
     }
+
+    @Test
+    void testPlusZeroAndPositiveRealNumbers() {
+        for (int i = 0; i < 100; i += 4) {
+            assertEquals(Quarter.Q1, Quarter.Q1.plus(i));
+            assertEquals(Quarter.Q2, Quarter.Q2.plus(i));
+            assertEquals(Quarter.Q3, Quarter.Q3.plus(i));
+            assertEquals(Quarter.Q4, Quarter.Q4.plus(i));
+        }
+        for (int i = 1; i < 100 + 1; i += 4) {
+            assertEquals(Quarter.Q2, Quarter.Q1.plus(i));
+            assertEquals(Quarter.Q3, Quarter.Q2.plus(i));
+            assertEquals(Quarter.Q4, Quarter.Q3.plus(i));
+            assertEquals(Quarter.Q1, Quarter.Q4.plus(i));
+        }
+        for (int i = 2; i < 100 + 2; i += 4) {
+            assertEquals(Quarter.Q3, Quarter.Q1.plus(i));
+            assertEquals(Quarter.Q4, Quarter.Q2.plus(i));
+            assertEquals(Quarter.Q1, Quarter.Q3.plus(i));
+            assertEquals(Quarter.Q2, Quarter.Q4.plus(i));
+        }
+        for (int i = 3; i < 100 + 3; i += 4) {
+            assertEquals(Quarter.Q4, Quarter.Q1.plus(i));
+            assertEquals(Quarter.Q1, Quarter.Q2.plus(i));
+            assertEquals(Quarter.Q2, Quarter.Q3.plus(i));
+            assertEquals(Quarter.Q3, Quarter.Q4.plus(i));
+        }
+    }
+
+    @Test
+    void testPlusZeroAndNegativeNumber() {
+        for (int i = 0; i > -100; i -= 4) {
+            assertEquals(Quarter.Q1, Quarter.Q1.plus(i));
+            assertEquals(Quarter.Q2, Quarter.Q2.plus(i));
+            assertEquals(Quarter.Q3, Quarter.Q3.plus(i));
+            assertEquals(Quarter.Q4, Quarter.Q4.plus(i));
+        }
+        for (int i = -1; i > -(100 + 1); i -= 4) {
+            assertEquals(Quarter.Q4, Quarter.Q1.plus(i));
+            assertEquals(Quarter.Q1, Quarter.Q2.plus(i));
+            assertEquals(Quarter.Q2, Quarter.Q3.plus(i));
+            assertEquals(Quarter.Q3, Quarter.Q4.plus(i));
+        }
+        for (int i = -2; i > -(100 + 2); i -= 4) {
+            assertEquals(Quarter.Q3, Quarter.Q1.plus(i));
+            assertEquals(Quarter.Q4, Quarter.Q2.plus(i));
+            assertEquals(Quarter.Q1, Quarter.Q3.plus(i));
+            assertEquals(Quarter.Q2, Quarter.Q4.plus(i));
+        }
+        for (int i = -3; i > -(100 + 3); i -= 4) {
+            assertEquals(Quarter.Q2, Quarter.Q1.plus(i));
+            assertEquals(Quarter.Q3, Quarter.Q2.plus(i));
+            assertEquals(Quarter.Q4, Quarter.Q3.plus(i));
+            assertEquals(Quarter.Q1, Quarter.Q4.plus(i));
+        }
+    }
+
+    @Test
+    void testMinusZeroAndNegativeNumber() {
+        for (int i = 0; i < 100; i += 4) {
+            assertEquals(Quarter.Q1, Quarter.Q1.minus(i));
+            assertEquals(Quarter.Q2, Quarter.Q2.minus(i));
+            assertEquals(Quarter.Q3, Quarter.Q3.minus(i));
+            assertEquals(Quarter.Q4, Quarter.Q4.minus(i));
+        }
+        for (int i = 1; i < 100 + 1; i += 4) {
+            assertEquals(Quarter.Q4, Quarter.Q1.minus(i));
+            assertEquals(Quarter.Q1, Quarter.Q2.minus(i));
+            assertEquals(Quarter.Q2, Quarter.Q3.minus(i));
+            assertEquals(Quarter.Q3, Quarter.Q4.minus(i));
+        }
+        for (int i = 2; i < 100 + 2; i += 4) {
+            assertEquals(Quarter.Q3, Quarter.Q1.minus(i));
+            assertEquals(Quarter.Q4, Quarter.Q2.minus(i));
+            assertEquals(Quarter.Q1, Quarter.Q3.minus(i));
+            assertEquals(Quarter.Q2, Quarter.Q4.minus(i));
+        }
+        for (int i = 3; i < 100 + 3; i += 4) {
+            assertEquals(Quarter.Q2, Quarter.Q1.minus(i));
+            assertEquals(Quarter.Q3, Quarter.Q2.minus(i));
+            assertEquals(Quarter.Q4, Quarter.Q3.minus(i));
+            assertEquals(Quarter.Q1, Quarter.Q4.minus(i));
+        }
+    }
+
+    @Test
+    void testMinusZeroAndPositiveRealNumbers() {
+        for (int i = 0; i > -100; i -= 4) {
+            assertEquals(Quarter.Q1, Quarter.Q1.minus(i));
+            assertEquals(Quarter.Q2, Quarter.Q2.minus(i));
+            assertEquals(Quarter.Q3, Quarter.Q3.minus(i));
+            assertEquals(Quarter.Q4, Quarter.Q4.minus(i));
+        }
+        for (int i = -1; i > -(100 + 1); i -= 4) {
+            assertEquals(Quarter.Q2, Quarter.Q1.minus(i));
+            assertEquals(Quarter.Q3, Quarter.Q2.minus(i));
+            assertEquals(Quarter.Q4, Quarter.Q3.minus(i));
+            assertEquals(Quarter.Q1, Quarter.Q4.minus(i));
+        }
+        for (int i = -2; i > -(100 + 2); i -= 4) {
+            assertEquals(Quarter.Q3, Quarter.Q1.minus(i));
+            assertEquals(Quarter.Q4, Quarter.Q2.minus(i));
+            assertEquals(Quarter.Q1, Quarter.Q3.minus(i));
+            assertEquals(Quarter.Q2, Quarter.Q4.minus(i));
+        }
+        for (int i = -3; i > -(100 + 3); i -= 4) {
+            assertEquals(Quarter.Q4, Quarter.Q1.minus(i));
+            assertEquals(Quarter.Q1, Quarter.Q2.minus(i));
+            assertEquals(Quarter.Q2, Quarter.Q3.minus(i));
+            assertEquals(Quarter.Q3, Quarter.Q4.minus(i));
+        }
+    }
 }