diff --git a/core/src/main/java/org/apache/calcite/sql/SqlKind.java b/core/src/main/java/org/apache/calcite/sql/SqlKind.java
index 3b11ac5cecb..381531a82bc 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlKind.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlKind.java
@@ -442,7 +442,7 @@ public enum SqlKind {
   /** {@code LEAST} function (Oracle). */
   LEAST,
 
-  /** {@code DATE_DIFF} function (BigQuery Semantics). */
+  /** {@code DATE_ADD} function (BigQuery Semantics). */
   DATE_ADD,
 
   /** {@code DATE_TRUNC} function (BigQuery). */
diff --git a/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java b/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java
index 51b19b26cb7..f9722692cee 100644
--- a/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java
+++ b/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java
@@ -11914,6 +11914,42 @@ void testTimestampDiff(boolean coercionEnabled) {
     f.checkNull("time_sub(CAST(NULL AS TIME), interval 5 minute)");
   }
 
+  @Test void testDateAdd() {
+    final SqlOperatorFixture f0 = fixture()
+        .setFor(SqlLibraryOperators.DATE_ADD);
+    f0.checkFails("^date_add(date '2008-12-25', "
+            + "interval 5 day)^",
+        "No match found for function signature "
+            + "DATE_ADD\\(<DATE>, <INTERVAL_DAY_TIME>\\)", false);
+
+    final SqlOperatorFixture f = f0.withLibrary(SqlLibrary.BIG_QUERY);
+    f.checkScalar("date_add(date '2016-02-22', interval 2 day)",
+        "2016-02-24",
+        "DATE NOT NULL");
+    f.checkScalar("date_add(date '2016-02-17', interval 1 week)",
+        "2016-02-24",
+        "DATE NOT NULL");
+    f.checkScalar("date_add(date '2016-02-10', interval 2 weeks)",
+        "2016-02-24",
+        "DATE NOT NULL");
+    f.checkScalar("date_add(date '2020-10-17', interval 0 week)",
+        "2020-10-17",
+        "DATE NOT NULL");
+    f.checkScalar("date_add(date '2016-11-24', interval 3 month)",
+        "2017-02-24",
+        "DATE NOT NULL");
+    f.checkScalar("date_add(date '2015-11-24', interval 1 quarter)",
+        "2016-02-24",
+        "DATE NOT NULL");
+    f.checkScalar("date_add(date '2015-08-24', interval 2 quarters)",
+        "2016-02-24",
+        "DATE NOT NULL");
+    f.checkScalar("date_add(date '2011-02-24', interval 5 year)",
+        "2016-02-24",
+        "DATE NOT NULL");
+    f.checkNull("date_add(CAST(NULL AS DATE), interval 5 day)");
+  }
+
   @Test void testDateSub() {
     final SqlOperatorFixture f0 = fixture()
         .setFor(SqlLibraryOperators.DATE_SUB);
@@ -12003,6 +12039,25 @@ void testTimestampDiff(boolean coercionEnabled) {
     f.checkFails("datediff(^\"MONTH\"^, '2019-09-14',  '2019-09-15')",
         "(?s)Column 'MONTH' not found in any table",
         false);
+    final SqlOperatorFixture f0 = f.withLibrary(SqlLibrary.BIG_QUERY);
+    f0.checkScalar("date_diff(DATE '2010-07-07', DATE '2008-12-25', DAY)",
+        "559",
+        "INTEGER NOT NULL");
+    f0.checkScalar("date_diff(DATE '2010-07-14', DATE '2010-07-07', WEEK)",
+        "1",
+        "INTEGER NOT NULL");
+    f0.checkScalar("date_diff(DATE '2011-12-14', DATE '2011-07-14', MONTH)",
+        "5",
+        "INTEGER NOT NULL");
+    f0.checkScalar("date_diff(DATE '2011-10-14', DATE '2011-07-14', QUARTER)",
+        "1",
+        "INTEGER NOT NULL");
+    f0.checkScalar("date_diff(DATE '2021-07-14', DATE '2011-07-14', YEAR)",
+        "10",
+        "INTEGER NOT NULL");
+    f0.checkNull("date_diff(CAST(NULL AS DATE), CAST(NULL AS DATE), DAY)");
+    f0.checkNull("date_diff(DATE '2008-12-25', CAST(NULL AS DATE), DAY)");
+    f0.checkNull("date_diff(CAST(NULL AS DATE), DATE '2008-12-25', DAY)");
   }
 
   /** Tests BigQuery's {@code TIME_ADD}, which adds an interval to a time