Add Projection Test

api/src/test/java/org/apache/iceberg/transforms/TestStartsWithProjection.java

@@ -0,0 +1,41 @@
+package org.apache.iceberg.transforms;
+
+import org.apache.iceberg.PartitionSpec;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.expressions.Expression;
+import org.apache.iceberg.expressions.Literal;
+import org.apache.iceberg.expressions.Projections;
+import org.apache.iceberg.expressions.UnboundPredicate;
+import org.apache.iceberg.types.Types;
+import org.junit.Assert;
+import org.junit.Test;
+
+import static org.apache.iceberg.TestHelpers.assertAndUnwrapUnbound;
+import static org.apache.iceberg.expressions.Expressions.startsWith;
+import static org.apache.iceberg.types.Types.NestedField.optional;
+
+public class TestStartsWithProjection {
+    private static final Schema SCHEMA = new Schema(optional(1, "someStringCol", Types.StringType.get()));
+    @Test
+    public void assertTruncateProjections(){
+        PartitionSpec spec = PartitionSpec.builderFor(SCHEMA).truncate("someStringCol", 4).build();
+
+        assertTruncateProjectionInclusive(spec, startsWith("someStringCol", "ab"), "ab");
+        assertTruncateProjectionInclusive(spec, startsWith("someStringCol", "abab"), "abab");
+        assertTruncateProjectionInclusive(spec, startsWith("someStringCol", "ababab"), "abab");
+
+    }
+
+    private void assertTruncateProjectionInclusive(PartitionSpec spec, UnboundPredicate<?> filter,
+                                                   String expectedLiteral) {
+        Expression projection = Projections.inclusive(spec).project(filter);
+        UnboundPredicate<?> predicate = assertAndUnwrapUnbound(projection);
+
+        Assert.assertEquals(predicate.op(), Expression.Operation.STARTS_WITH);
+
+        Literal literal = predicate.literal();
+        Truncate<CharSequence> transform = (Truncate<CharSequence>) spec.getFieldsBySourceId(1).get(0).transform();
+        String output = transform.toHumanString((String) literal.value());
+        Assert.assertEquals(expectedLiteral, output);
+    }
+}