fix: Add unit tests for date format and parsing

core/src/test/java/tech/tablesaw/io/csv/CsvReaderTest.java

@@ -21,7 +21,16 @@
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
-import static tech.tablesaw.api.ColumnType.*;
+import static tech.tablesaw.api.ColumnType.BOOLEAN;
+import static tech.tablesaw.api.ColumnType.DOUBLE;
+import static tech.tablesaw.api.ColumnType.FLOAT;
+import static tech.tablesaw.api.ColumnType.INTEGER;
+import static tech.tablesaw.api.ColumnType.LOCAL_DATE;
+import static tech.tablesaw.api.ColumnType.LOCAL_DATE_TIME;
+import static tech.tablesaw.api.ColumnType.LOCAL_TIME;
+import static tech.tablesaw.api.ColumnType.SHORT;
+import static tech.tablesaw.api.ColumnType.SKIP;
+import static tech.tablesaw.api.ColumnType.STRING;
 
 import com.google.common.collect.ImmutableMap;
 import com.univocity.parsers.common.TextParsingException;
@@ -398,6 +407,83 @@ public void testDateDetection1() {
     assertEquals(Collections.singletonList(LOCAL_TIME), actual);
   }
 
+  /** Asserts ISO and US date formats are supported, while EU date format is not by default. */
+  @Test
+  public void testDateDetection2() {
+
+    final Reader reader =
+        new StringReader(
+            "DateISO,DateUS,DateEU"
+                + LINE_END
+                + "2024-03-20,03/20/2024,20/03/2024"
+                + LINE_END
+                + "2024-03-26,03/26/2024,26/03/2024"
+                + LINE_END);
+
+    final boolean header = true;
+
+    CsvReadOptions options = CsvReadOptions.builder(reader).header(header).build();
+
+    final List<ColumnType> actual = asList(new CsvReader().detectColumnTypes(reader, options));
+    assertEquals(List.of(LOCAL_DATE, LOCAL_DATE, STRING), actual);
+  }
+
+  /**
+   * Asserts ISO dates > {@code LOCAL_DATE} and US dates > {@code STRING} for date format {@code
+   * yyyy-MM-dd}.
+   */
+  @Test
+  public void testDateDetectionIsoDate() {
+
+    final Reader reader =
+        new StringReader(
+            "DateISO,DateUS,DateEU"
+                + LINE_END
+                + "2024-03-20,03/20/2024"
+                + LINE_END
+                + "2024-03-26,03/26/2024"
+                + LINE_END);
+
+    final boolean header = true;
+
+    CsvReadOptions options =
+        CsvReadOptions.builder(reader)
+            .header(header)
+            .dateFormat(DateTimeFormatter.ofPattern("yyyy-MM-dd"))
+            .build();
+
+    final List<ColumnType> actual = asList(new CsvReader().detectColumnTypes(reader, options));
+    assertEquals(List.of(LOCAL_DATE, STRING), actual);
+  }
+
+  /**
+   * Asserts ISO dates > {@code STRING} and US dates > {@code LOCAL_DATE} for date format {@code
+   * MM/dd/yyyy}.
+   */
+  @Test
+  public void testDateDetectionUsDate() {
+
+    final Reader reader =
+        new StringReader(
+            "DateISO,DateUS,DateEU"
+                + LINE_END
+                + "2024-03-20,03/20/2024"
+                + LINE_END
+                + "2024-03-26,03/26/2024"
+                + LINE_END);
+
+    final boolean header = true;
+
+    CsvReadOptions options =
+        CsvReadOptions.builder(reader)
+            .header(header)
+            .dateFormat(DateTimeFormatter.ofPattern("MM/dd/yyyy"))
+            .build();
+
+    final List<ColumnType> actual = asList(new CsvReader().detectColumnTypes(reader, options));
+    assertEquals(List.of(STRING, LOCAL_DATE), actual);
+  }
+
   @Test
   public void testTimeDetection1() {