Add tests for schema inference of leading zeros and decimals

Renamed and updated the test for leading zeros to clarify that such values are parsed as integers, not strings, and added assertions for inferred types. Introduced a new test to verify that decimal values without an integer part are correctly inferred as decimals and that their scale is accurately determined.

Author: potatoqualitee

project/dbatools.Tests/Csv/CsvSchemaInferenceTest.cs

@@ -515,7 +515,7 @@ public void TestInferSchema_QuotedFields()
         }
 
         [TestMethod]
-        public void TestInferSchema_LeadingZeros_TreatedAsString()
+        public void TestInferSchema_LeadingZeros_ParseAsInteger()
         {
             string csvPath = Path.Combine(_tempDir, "leadingzeros.csv");
             File.WriteAllText(csvPath, @"ZipCode,Phone
@@ -525,10 +525,34 @@ public void TestInferSchema_LeadingZeros_TreatedAsString()
 
             var columns = CsvSchemaInference.InferSchemaFromSample(csvPath);
 
-            // Leading zeros should preserve as integer since parsing ignores them
-            // but this tests that we handle them gracefully
-            Assert.IsNotNull(columns[0].SqlDataType);
-            Assert.IsNotNull(columns[1].SqlDataType);
+            // Leading zeros are parsed successfully by int.TryParse (01234 -> 1234)
+            // so the column is inferred as integer. Note: the leading zeros are NOT
+            // preserved in the parsed value. If preserving leading zeros is required,
+            // callers should override the inferred type to varchar.
+            Assert.AreEqual("int", columns[0].SqlDataType);
+            Assert.AreEqual("int", columns[1].SqlDataType); // 0123456789 fits in int (< 2.1 billion)
+        }
+
+        [TestMethod]
+        public void TestInferSchema_DecimalWithNoIntegerPart()
+        {
+            string csvPath = Path.Combine(_tempDir, "decimalnoint.csv");
+            File.WriteAllText(csvPath, @"Value,Tiny,Mixed
+.5,.001,.999
+.25,.002,1.5
+.125,.003,10.25
+");
+
+            var columns = CsvSchemaInference.InferSchemaFromSample(csvPath);
+
+            // Decimals without integer part (e.g., .5 instead of 0.5) should be handled
+            Assert.IsTrue(columns[0].SqlDataType.Contains("decimal"), $"Expected decimal, got {columns[0].SqlDataType}");
+            Assert.IsTrue(columns[1].SqlDataType.Contains("decimal"), $"Expected decimal, got {columns[1].SqlDataType}");
+            Assert.IsTrue(columns[2].SqlDataType.Contains("decimal"), $"Expected decimal, got {columns[2].SqlDataType}");
+
+            // Verify scale is tracked correctly
+            Assert.AreEqual(3, columns[0].Scale); // .5, .25, .125 -> max 3 digits after decimal
+            Assert.AreEqual(3, columns[1].Scale); // .001, .002, .003 -> 3 digits after decimal
         }
 
         #endregion