Address Eduard's feedback: Add unit tests and enable tests across Spark versions

- Add unit tests in api module for string-to-binary and string-to-fixed conversions
  - Test valid hex string conversions (uppercase and lowercase)
  - Test invalid hex strings return null
  - Test fixed type with wrong length returns null
- Remove @disabled testBinaryInFilter from Spark v3.4, v3.5, and v4.0
  - The fix in Literals.java now properly handles binary/fixed types
  - Tests should work across all Spark versions

Author: sfc-gh-prsingh

api/src/test/java/org/apache/iceberg/expressions/TestMiscLiteralConversions.java

@@ -107,6 +107,62 @@ public void testFixedToBinary() {
         .isEqualTo(lit.value().duplicate());
   }
 
+  @Test
+  public void testStringToFixed() {
+    // Test valid hex string to fixed conversion
+    Literal<CharSequence> hexString = Literal.of("000102");
+    Literal<ByteBuffer> fixedLit = hexString.to(Types.FixedType.ofLength(3));
+    assertThat(fixedLit).as("Should convert valid hex string to fixed").isNotNull();
+    assertThat(fixedLit.value().array())
+        .as("Should decode hex string correctly")
+        .isEqualTo(new byte[] {0, 1, 2});
+
+    // Test lowercase hex string
+    Literal<CharSequence> lowercaseHex = Literal.of("0a0b0c");
+    Literal<ByteBuffer> lowercaseFixed = lowercaseHex.to(Types.FixedType.ofLength(3));
+    assertThat(lowercaseFixed).as("Should convert lowercase hex string to fixed").isNotNull();
+    assertThat(lowercaseFixed.value().array())
+        .as("Should decode lowercase hex string correctly")
+        .isEqualTo(new byte[] {10, 11, 12});
+
+    // Test wrong length returns null
+    Literal<CharSequence> wrongLength = Literal.of("0001");
+    assertThat(wrongLength.to(Types.FixedType.ofLength(3)))
+        .as("Should return null for wrong length")
+        .isNull();
+
+    // Test invalid hex string returns null
+    Literal<CharSequence> invalidHex = Literal.of("GGHHII");
+    assertThat(invalidHex.to(Types.FixedType.ofLength(3)))
+        .as("Should return null for invalid hex string")
+        .isNull();
+  }
+
+  @Test
+  public void testStringToBinary() {
+    // Test valid hex string to binary conversion
+    Literal<CharSequence> hexString = Literal.of("000102");
+    Literal<ByteBuffer> binaryLit = hexString.to(Types.BinaryType.get());
+    assertThat(binaryLit).as("Should convert valid hex string to binary").isNotNull();
+    assertThat(binaryLit.value().array())
+        .as("Should decode hex string correctly")
+        .isEqualTo(new byte[] {0, 1, 2});
+
+    // Test lowercase hex string
+    Literal<CharSequence> lowercaseHex = Literal.of("0a0b0c");
+    Literal<ByteBuffer> lowercaseBinary = lowercaseHex.to(Types.BinaryType.get());
+    assertThat(lowercaseBinary).as("Should convert lowercase hex string to binary").isNotNull();
+    assertThat(lowercaseBinary.value().array())
+        .as("Should decode lowercase hex string correctly")
+        .isEqualTo(new byte[] {10, 11, 12});
+
+    // Test invalid hex string returns null
+    Literal<CharSequence> invalidHex = Literal.of("GGHHII");
+    assertThat(invalidHex.to(Types.BinaryType.get()))
+        .as("Should return null for invalid hex string")
+        .isNull();
+  }
+
   @Test
   public void testInvalidBooleanConversions() {
     testInvalidConversions(

spark/v3.4/spark-extensions/src/test/java/org/apache/iceberg/spark/extensions/TestRemoteScanPlanning.java

@@ -25,8 +25,6 @@
 import org.apache.iceberg.rest.RESTCatalogProperties;
 import org.apache.iceberg.spark.SparkCatalogConfig;
 import org.apache.iceberg.spark.sql.TestSelect;
-import org.junit.jupiter.api.Disabled;
-import org.junit.jupiter.api.TestTemplate;
 import org.junit.jupiter.api.extension.ExtendWith;
 
 @ExtendWith(ParameterizedTestExtension.class)
@@ -48,11 +46,4 @@ protected static Object[][] parameters() {
       }
     };
   }
-
-  @TestTemplate
-  @Disabled(
-      "binary filter that is used by Spark is not working because ExpressionParser.fromJSON doesn't have the Schema to properly parse the filter expression")
-  public void testBinaryInFilter() {
-    super.testBinaryInFilter();
-  }
 }

spark/v3.5/spark-extensions/src/test/java/org/apache/iceberg/spark/extensions/TestRemoteScanPlanning.java

@@ -25,8 +25,6 @@
 import org.apache.iceberg.rest.RESTCatalogProperties;
 import org.apache.iceberg.spark.SparkCatalogConfig;
 import org.apache.iceberg.spark.sql.TestSelect;
-import org.junit.jupiter.api.Disabled;
-import org.junit.jupiter.api.TestTemplate;
 import org.junit.jupiter.api.extension.ExtendWith;
 
 @ExtendWith(ParameterizedTestExtension.class)
@@ -48,11 +46,4 @@ protected static Object[][] parameters() {
       }
     };
   }
-
-  @TestTemplate
-  @Disabled(
-      "binary filter that is used by Spark is not working because ExpressionParser.fromJSON doesn't have the Schema to properly parse the filter expression")
-  public void testBinaryInFilter() {
-    super.testBinaryInFilter();
-  }
 }

spark/v4.0/spark-extensions/src/test/java/org/apache/iceberg/spark/extensions/TestRemoteScanPlanning.java

@@ -25,8 +25,6 @@
 import org.apache.iceberg.rest.RESTCatalogProperties;
 import org.apache.iceberg.spark.SparkCatalogConfig;
 import org.apache.iceberg.spark.sql.TestSelect;
-import org.junit.jupiter.api.Disabled;
-import org.junit.jupiter.api.TestTemplate;
 import org.junit.jupiter.api.extension.ExtendWith;
 
 @ExtendWith(ParameterizedTestExtension.class)
@@ -48,11 +46,4 @@ protected static Object[][] parameters() {
       }
     };
   }
-
-  @TestTemplate
-  @Disabled(
-      "binary filter that is used by Spark is not working because ExpressionParser.fromJSON doesn't have the Schema to properly parse the filter expression")
-  public void testBinaryInFilter() {
-    super.testBinaryInFilter();
-  }
 }