test: add MSat unit tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ovitrif

app/src/test/java/to/bitkit/models/MSatTest.kt

@@ -0,0 +1,78 @@
+package to.bitkit.models
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class MSatTest {
+
+    // region ceil
+    @Test
+    fun `ceil returns exact sat for multiple of 1000`() {
+        assertEquals(1uL, MSat(1000uL).ceil())
+    }
+
+    @Test
+    fun `ceil rounds up for non-multiple`() {
+        assertEquals(2uL, MSat(1001uL).ceil())
+    }
+
+    @Test
+    fun `ceil rounds up for 1 msat`() {
+        assertEquals(1uL, MSat(1uL).ceil())
+    }
+
+    @Test
+    fun `ceil rounds up for 999 msat`() {
+        assertEquals(1uL, MSat(999uL).ceil())
+    }
+
+    @Test
+    fun `ceil returns zero for zero`() {
+        assertEquals(0uL, MSat(0uL).ceil())
+    }
+
+    @Test
+    fun `ceil handles realistic payment amount`() {
+        assertEquals(223uL, MSat(222_222uL).ceil())
+    }
+    // endregion
+
+    // region floor
+    @Test
+    fun `floor returns exact sat for multiple of 1000`() {
+        assertEquals(2uL, MSat(2000uL).floor())
+    }
+
+    @Test
+    fun `floor truncates for non-multiple`() {
+        assertEquals(1uL, MSat(1999uL).floor())
+    }
+
+    @Test
+    fun `floor returns zero for sub-sat value`() {
+        assertEquals(0uL, MSat(999uL).floor())
+    }
+
+    @Test
+    fun `floor returns zero for zero`() {
+        assertEquals(0uL, MSat(0uL).floor())
+    }
+
+    @Test
+    fun `floor handles realistic fee amount`() {
+        assertEquals(222uL, MSat(222_222uL).floor())
+    }
+    // endregion
+
+    // region sugar functions
+    @Test
+    fun `msatCeilOf matches MSat ceil`() {
+        assertEquals(MSat(1500uL).ceil(), msatCeilOf(1500uL))
+    }
+
+    @Test
+    fun `msatFloorOf matches MSat floor`() {
+        assertEquals(MSat(1500uL).floor(), msatFloorOf(1500uL))
+    }
+    // endregion
+}