From a7a95594944a4bb12fed403ad6448e8d21e15321 Mon Sep 17 00:00:00 2001
From: Mariusz Pacek <pacekm90@gmail.com>
Date: Sat, 27 Dec 2025 11:13:21 +0100
Subject: [PATCH] test(modbus): add parser tests for 4-byte and legacy-wrap
 decoding

---
 .../automation/modbus/ModbusParserTests.java  | 89 +++++++++++++++++++
 1 file changed, 89 insertions(+)
 create mode 100644 src/test/java/home/automation/modbus/ModbusParserTests.java

diff --git a/src/test/java/home/automation/modbus/ModbusParserTests.java b/src/test/java/home/automation/modbus/ModbusParserTests.java
new file mode 100644
index 0000000..870d0c7
--- /dev/null
+++ b/src/test/java/home/automation/modbus/ModbusParserTests.java
@@ -0,0 +1,89 @@
+package home.automation.modbus;
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Method;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ModbusParserTests {
+
+    private ModbusRtuTcpRepository createRepo() {
+        return new ModbusRtuTcpRepository(new Connection() {
+            @Override
+            public com.serotonin.modbus4j.ModbusMaster getConnection() {
+                throw new UnsupportedOperationException("not used in parser tests");
+            }
+        }, java.util.Collections.emptyList());
+    }
+
+    private String invokeDecode(ModbusRtuTcpRepository repo, short[] data, String dataType, Double scale, Boolean legacy) throws Exception {
+        Method m = ModbusRtuTcpRepository.class.getDeclaredMethod("decodeValueFromShorts", short[].class, String.class, Double.class, Boolean.class);
+        m.setAccessible(true);
+        return (String) m.invoke(repo, (Object) data, dataType, scale, legacy);
+    }
+
+    @Test
+    void decodeFourByteFloat() throws Exception {
+        ModbusRtuTcpRepository repo = createRepo();
+        float value = 12.34f;
+        int bits = Float.floatToIntBits(value);
+        short high = (short) ((bits >>> 16) & 0xFFFF);
+        short low = (short) (bits & 0xFFFF);
+        String decoded = invokeDecode(repo, new short[]{high, low}, "FOUR_BYTE_FLOAT", 1.0, null);
+        assertEquals("12.34", decoded);
+    }
+
+    @Test
+    void decodeFourByteFloatSwapped() throws Exception {
+        ModbusRtuTcpRepository repo = createRepo();
+        float value = -5.5f;
+        int bits = Float.floatToIntBits(value);
+        short high = (short) ((bits >>> 16) & 0xFFFF);
+        short low = (short) (bits & 0xFFFF);
+        // swapped: pass low first, then high and use SWAPPED dataType
+        String decoded = invokeDecode(repo, new short[]{low, high}, "FOUR_BYTE_FLOAT_SWAPPED", 1.0, null);
+        // rounding to 2 decimals expected by implementation
+        assertEquals("-5.5", decoded);
+    }
+
+    @Test
+    void decodeFourByteUnsignedInt() throws Exception {
+        ModbusRtuTcpRepository repo = createRepo();
+        long unsignedVal = 3000000000L; // > 2^31
+        int bits = (int) unsignedVal; // low 32 bits
+        short high = (short) ((bits >>> 16) & 0xFFFF);
+        short low = (short) (bits & 0xFFFF);
+        String decoded = invokeDecode(repo, new short[]{high, low}, "FOUR_BYTE_INT_UNSIGNED", 1.0, null);
+        assertEquals((double) unsignedVal, Double.parseDouble(decoded), 0.0001);
+    }
+
+    @Test
+    void decodeFourByteSignedInt() throws Exception {
+        ModbusRtuTcpRepository repo = createRepo();
+        int signedVal = -12345678;
+        int bits = signedVal;
+        short high = (short) ((bits >>> 16) & 0xFFFF);
+        short low = (short) (bits & 0xFFFF);
+        String decoded = invokeDecode(repo, new short[]{high, low}, "FOUR_BYTE_INT_SIGNED", 1.0, null);
+        assertEquals((double) signedVal, Double.parseDouble(decoded), 0.0001);
+    }
+
+    @Test
+    void decodeTwoByteSignedLegacyWrap() throws Exception {
+        ModbusRtuTcpRepository repo = createRepo();
+        short s = (short) (-32760); // near legacy wrap sentinel
+        String decoded = invokeDecode(repo, new short[]{s}, "TWO_BYTE_INT_SIGNED", 1.0, true);
+        // calculation: -(s + 32768) * scale -> -( -32760 + 32768) = -8
+        assertEquals("-8.0", decoded);
+    }
+
+    @Test
+    void decodeTwoByteNormal() throws Exception {
+        ModbusRtuTcpRepository repo = createRepo();
+        short s = (short) (123); 
+        String decoded = invokeDecode(repo, new short[]{s}, "TWO_BYTE_INT_SIGNED", 0.1, false);
+        // 123 * 0.1 = 12.3
+        assertEquals("12.3", decoded);
+    }
+}
-- 
2.54.0