chore: Increase coverage in CustomFeeExemptions (#13233)

Signed-off-by: Thomas Moran <152873392+thomas-swirlds-labs@users.noreply.github.com>

hedera-node/hedera-token-service-impl/src/test/java/com/hedera/node/app/service/token/impl/handlers/transfer/customfees/CustomFeeExemptionsTest.java

@@ -0,0 +1,181 @@
+/*
+ * Copyright (C) 2024 Hedera Hashgraph, LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.hedera.node.app.service.token.impl.handlers.transfer.customfees;
+
+import static com.hedera.node.app.service.token.impl.handlers.BaseCryptoHandler.asAccount;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.hedera.hapi.node.base.AccountID;
+import com.hedera.hapi.node.base.TokenID;
+import com.hedera.hapi.node.base.TokenType;
+import com.hedera.hapi.node.state.token.Token;
+import com.hedera.hapi.node.transaction.CustomFee;
+import com.hedera.node.app.service.token.impl.test.handlers.util.TokenHandlerTestBase;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class CustomFeeExemptionsTest extends TokenHandlerTestBase {
+
+    private Token treasuryToken;
+    private Token nonTreasuryToken;
+    private final TokenID tokenId = TokenID.newBuilder().tokenNum(1000).build();
+    private final AccountID feeCollector = asAccount(7001);
+    private final AccountID minter = asAccount(2001);
+    private final AccountID sender = asAccount(4001);
+    private final CustomFee customFee = CustomFee.newBuilder()
+            .fixedFee(fixedFee)
+            .feeCollectorAccountId(feeCollector)
+            .fractionalFee(fractionalFee)
+            .royaltyFee(royaltyFee)
+            .build();
+
+    private final CustomFee customFeeCollectorSender = CustomFee.newBuilder()
+            .fixedFee(fixedFee)
+            .feeCollectorAccountId(sender)
+            .fractionalFee(fractionalFee)
+            .royaltyFee(royaltyFee)
+            .build();
+
+    @BeforeEach
+    void setUp() {
+        treasuryToken = Token.newBuilder()
+                .tokenId(tokenId)
+                .treasuryAccountId(sender)
+                .customFees(customFee)
+                .tokenType(TokenType.FUNGIBLE_COMMON)
+                .build();
+        nonTreasuryToken = Token.newBuilder()
+                .tokenId(tokenId)
+                .treasuryAccountId(feeCollector)
+                .customFees(customFee)
+                .tokenType(TokenType.FUNGIBLE_COMMON)
+                .build();
+    }
+
+    @Test
+    void testCoverageOfPrivateConstructor()
+            throws NoSuchMethodException, InstantiationException, IllegalAccessException {
+        final Constructor<CustomFeeExemptions> constructor = CustomFeeExemptions.class.getDeclaredConstructor();
+        constructor.setAccessible(true);
+        try {
+            constructor.newInstance();
+        } catch (InvocationTargetException e) {
+            Throwable cause = e.getCause();
+            assertThat(cause.getClass()).isEqualTo(UnsupportedOperationException.class);
+        }
+    }
+
+    @Test
+    void testPayerExemptWhenPayerIsTokenTreasury() {
+        CustomFeeMeta customFeeMetaFromTreasury = CustomFeeMeta.customFeeMetaFrom(treasuryToken);
+        assertThat(CustomFeeExemptions.isPayerExempt(customFeeMetaFromTreasury, customFee, sender))
+                .isTrue();
+    }
+
+    @Test
+    void testPayerExemptWhenPayerIsTheFeeCollector() {
+        CustomFeeMeta customFeeMeta = CustomFeeMeta.customFeeMetaFrom(nonTreasuryToken);
+        assertThat(CustomFeeExemptions.isPayerExempt(customFeeMeta, customFeeCollectorSender, sender))
+                .isTrue();
+    }
+
+    @Test
+    void testSomePayersExemptWhenPayerCollectorForAnyFee() {
+        final var customFee1 = CustomFee.newBuilder()
+                .feeCollectorAccountId(feeCollector)
+                .fixedFee(fixedFee)
+                .build();
+        final var customFee2 = CustomFee.newBuilder()
+                .feeCollectorAccountId(sender)
+                .fixedFee(fixedFee)
+                .build();
+        final var customFeeMeta =
+                new CustomFeeMeta(tokenId, minter, List.of(customFee1, customFee2), TokenType.FUNGIBLE_COMMON);
+        assertThat(CustomFeeExemptions.isPayerExempt(customFeeMeta, customFeeCollectorSender, sender))
+                .isTrue();
+    }
+
+    @Test
+    void testAllPayersExemptWhenPayerCollectorForAnyFee() {
+        final var customFee1 = CustomFee.newBuilder()
+                .allCollectorsAreExempt(true)
+                .feeCollectorAccountId(sender)
+                .fixedFee(fixedFee)
+                .build();
+        final var customFee2 =
+                CustomFee.newBuilder().allCollectorsAreExempt(true).build();
+
+        final var customFeeCollector = CustomFee.newBuilder()
+                .feeCollectorAccountId(feeCollector)
+                .allCollectorsAreExempt(true)
+                .fixedFee(fixedFee)
+                .build();
+        final var customFeeMeta =
+                new CustomFeeMeta(tokenId, minter, List.of(customFee1, customFee2), TokenType.FUNGIBLE_COMMON);
+        assertThat(CustomFeeExemptions.isPayerExempt(customFeeMeta, customFeeCollector, sender))
+                .isTrue();
+    }
+
+    @Test
+    void testAllPayersExemptButPayerNotCollectorForAnyFee() {
+        final var customFee =
+                CustomFee.newBuilder().allCollectorsAreExempt(true).build();
+        final var customFeeCollector = CustomFee.newBuilder()
+                .feeCollectorAccountId(feeCollector)
+                .allCollectorsAreExempt(true)
+                .fixedFee(fixedFee)
+                .build();
+        final var customFeeMeta = new CustomFeeMeta(tokenId, minter, List.of(customFee), TokenType.FUNGIBLE_COMMON);
+        assertThat(CustomFeeExemptions.isPayerExempt(customFeeMeta, customFeeCollector, sender))
+                .isFalse();
+    }
+
+    @Test
+    void testPayerNotExemptWhenPayerIsNotCollectorForAnyFee() {
+        final var customFeeCollector = CustomFee.newBuilder()
+                .feeCollectorAccountId(feeCollector)
+                .fixedFee(fixedFee)
+                .build();
+        final var customFeeMeta =
+                new CustomFeeMeta(tokenId, minter, List.of(customFeeCollector), TokenType.FUNGIBLE_COMMON);
+        assertThat(CustomFeeExemptions.isPayerExempt(customFeeMeta, customFeeCollector, sender))
+                .isFalse();
+    }
+
+    @Test
+    void testAllCollectorsExemptAndPayerNotCollectorForAnyTokenFee() {
+        final var customFee1 = CustomFee.newBuilder()
+                .allCollectorsAreExempt(true)
+                .feeCollectorAccountId(minter)
+                .fixedFee(fixedFee)
+                .build();
+        final var customFee2 =
+                CustomFee.newBuilder().allCollectorsAreExempt(true).build();
+
+        final var customFeeCollector = CustomFee.newBuilder()
+                .feeCollectorAccountId(feeCollector)
+                .fixedFee(fixedFee)
+                .build();
+        final var customFeeMeta =
+                new CustomFeeMeta(tokenId, minter, List.of(customFee1, customFee2), TokenType.FUNGIBLE_COMMON);
+        assertThat(CustomFeeExemptions.isPayerExempt(customFeeMeta, customFeeCollector, sender))
+                .isFalse();
+    }
+}