tests/driver_tsl4531x: Add tests for illuminance sensor.

Missing README.

tests/driver_tsl4531x/Makefile

+BOARD ?= stm32f4discovery
+
+include ../Makefile.tests_common
+
+USEMODULE += tsl4531x
+USEMODULE += xtimer
+
+I2C_PORT ?= 0
+
+CFLAGS += -DTSL4531_I2C_PORT=$(I2C_PORT)
+
+include $(RIOTBASE)/Makefile.include

tests/driver_tsl4531x/main.c

+/*
+ * Copyright (C) 2016 Inria
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup tests
+ * @{
+ *
+ * @file
+ * @brief       Test application for the TSL2561 Lux sensor
+ *
+ * @author      Alexandre Abadie <alexandre.abadie@inria.fr>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+
+#include "xtimer.h"
+#include "periph/i2c.h"
+
+#include "tsl4531x.h"
+
+#define _100ms_in_us   (100 * 1000u) /* 1 second delay between printf */
+
+int main(void)
+{
+    tsl4531x_t dev;
+    int err;
+
+    puts("TSL4531x test application. Initializing...");
+
+    if((err = tsl4531x_init(&dev, TSL4531_I2C_PORT, TSL4531x_INTEGRATE_200ms)) < 0) {
+        printf("Error setting up device. %d (%s)\n", err, strerror(err));
+        return 1;
+    }
+
+    puts("Initialized, will begin measurements.");
+    while (1) {
+        int err;
+        uint16_t lux;
+
+        if ((err = tsl4531x_read(&dev, &lux)) < 0) {
+            printf("Error reading from device. %d (%s)\n", err, strerror(err));
+        } else {
+            printf("Illuminance [lx]: %u\n", lux);
+        }
+
+        xtimer_usleep(_100ms_in_us);
+    }
+
+    return 0;
+}