diff --git a/src/test/java/ru/rejchev/steamid/BitVector64Test.java b/src/test/java/ru/rejchev/steamid/BitVector64Test.java
new file mode 100644
index 0000000..7e7d36a
--- /dev/null
+++ b/src/test/java/ru/rejchev/steamid/BitVector64Test.java
@@ -0,0 +1,90 @@
+package ru.rejchev.steamid;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import ru.rejchev.steamid.containers.BitVector64;
+
+import java.util.Arrays;
+import java.util.function.LongUnaryOperator;
+
+public class BitVector64Test {
+
+    public static final long[] sourceData = {
+            0,
+            76561198092541763L,
+            Long.MAX_VALUE
+    };
+
+    @Test
+    void thatGet_0_0x0L_correct() {
+        final char offset = 0;
+        final long mask = 0x0L;
+
+        final long[] expectedData = { 0, 0, 0 };
+
+        assertArrayEquals(simpleGetMethodMapper(offset, mask), expectedData);
+    }
+
+    @Test
+    void thatGet_0_0xFL_correct() {
+        final char offset = 0;
+        final long mask = 0xFFFF_FFFF_FFFF_FFFFL;
+
+        assertArrayEquals(simpleGetMethodMapper(offset, mask), sourceData);
+    }
+
+    @Test
+    void thatGet_1_0xF_correct() {
+
+        final char offset = 1;
+        final long mask = 0xFFFF_FFFF_FFFF_FFFFL;
+
+        final long[] expected = { 0, 0x88_0000_83F1_2FA1L, 0x3FFF_FFFF_FFFF_FFFFL };
+
+        assertArrayEquals(simpleGetMethodMapper(offset, mask), expected);
+    }
+
+    void thatSet_s_0_0x0_correct() {
+        final char offset = 0;
+        final long mask = 0x0L;
+        final long value = 0x0000_FFFF_0000_FFFFL; // FFFF 0000 FFFF 0000
+
+        final long[] expected = sourceData;
+
+        // source[1]:
+        // ~(mask << offset) = 0xFFFF_FFFF_FFFF_FFFF
+        // (source & 0xFFFF_FFFF_FFFF_FFFF) = source
+        // ((value & mask) << offset = 0
+        // 0x0110_0000_07E2_0000 | 0 = 0x0110_0000_07E2_0000
+
+        // source[2]
+        // (source & 0xFFFF_FFFF_FFFF_FFFF) = source
+
+        Assertions.assertEquals(0, part1OfSetMethod(value, offset, mask));
+        assertArrayEquals(simpleSetMethodMapper(value, offset, mask), expected);
+    }
+
+    static LongUnaryOperator simpleGetMethodMapper(char offset, long mask) {
+        return operand -> (new BitVector64(operand)).get(offset, mask);
+    }
+
+    static LongUnaryOperator simpleSetMethodMapper(long value, char offset, long mask) {
+        return operand -> (new BitVector64(operand)).set(value, offset, mask).data();
+    }
+
+    void assertArrayEquals(LongUnaryOperator mapper, long[] expected) {
+        Assertions.assertArrayEquals(expected, Arrays.stream(BitVector64Test.sourceData).map(mapper).toArray());
+    }
+
+    long part1OfSetMethod(long value, char offset, long mask) {
+        return ((value & mask) << offset);
+    }
+
+    long part0OfSetMethod(long data, char offset, long mask) {
+        return (data & ~(mask << offset));
+    }
+
+    long combineSetMethod(long data, long value, char offset, long mask) {
+        return part0OfSetMethod(data, offset, mask) | part1OfSetMethod(value, offset, mask);
+    }
+}
diff --git a/src/test/java/ru/rejchev/steamid/SteamIDTest.java b/src/test/java/ru/rejchev/steamid/SteamIDTest.java
new file mode 100644
index 0000000..f1dec2c
--- /dev/null
+++ b/src/test/java/ru/rejchev/steamid/SteamIDTest.java
@@ -0,0 +1,24 @@
+package ru.rejchev.steamid;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+public class SteamIDTest {
+
+    public static final long[] source = {
+            76561198092541763L
+    };
+
+    @Test
+    void thatToString64Conversion_correct() {
+        Assertions.assertArrayEquals(sourceAsString(), Arrays.stream(source)
+                .mapToObj(x -> (new SteamID(x)).toString())
+                .toArray(String[]::new));
+    }
+
+    static String[] sourceAsString() {
+        return Arrays.stream(source).mapToObj(String::valueOf).toArray(String[]::new);
+    }
+}