encoding: add a hex sub-module (#11193)

vlib/encoding/hex/hex_test.v

@@ -0,0 +1,41 @@
+module hex
+
+fn test_decode() ? {
+	assert decode('') ? == []
+	assert decode('0') ? == [byte(0x0)]
+	assert decode('f') ? == [byte(0xf)]
+	assert decode('0f') ? == [byte(0x0f)]
+	assert decode('ff') ? == [byte(0xff)]
+	assert decode('123') ? == [byte(0x1), 0x23]
+	assert decode('1234') ? == [byte(0x12), 0x34]
+	assert decode('12345') ? == [byte(0x1), 0x23, 0x45]
+}
+
+fn test_decode_fails() ? {
+	if x := decode('foo') {
+		return error('expected decode to fail, got $x')
+	}
+	if x := decode('g') {
+		return error('expected decode to fail, got $x')
+	}
+	if x := decode('000000000g') {
+		return error('expected decode to fail, got $x')
+	}
+	if x := decode('_') {
+		return error('expected decode to fail, got $x')
+	}
+	if x := decode('!') {
+		return error('expected decode to fail, got $x')
+	}
+}
+
+fn test_encode() ? {
+	assert encode(decode('') ?) == ''
+	assert encode(decode('0') ?) == '00'
+	assert encode(decode('f') ?) == '0f'
+	assert encode(decode('0f') ?) == '0f'
+	assert encode(decode('ff') ?) == 'ff'
+	assert encode(decode('123') ?) == '0123'
+	assert encode(decode('1234') ?) == '1234'
+	assert encode(decode('12345') ?) == '012345'
+}