Replaced Sonar magic numbers with #defines. Added first cut of Sonar test code. Corrected spelling in comments. Minor improvements to comments.

src/test/unit/sonar_unittest.cc

@@ -0,0 +1,40 @@
+/*
+ * This file is part of Cleanflight.
+ *
+ * Cleanflight is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Cleanflight is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+
+extern "C" {
+    #include "drivers/sonar_hcsr04.h"
+    #include "sensors/sonar.h"
+    #include "build_config.h"
+}
+
+#include "unittest_macros.h"
+#include "gtest/gtest.h"
+
+TEST(SonarUnittest, TestConstants)
+{
+    // SONAR_OUT_OF_RANGE must be negative
+    EXPECT_LE(SONAR_OUT_OF_RANGE, 0);
+    // Check reasonable values for maximum tilt
+    EXPECT_GE(SONAR_MAX_TILT_ANGLE, 0);
+    EXPECT_LE(SONAR_MAX_TILT_ANGLE, 450);
+    // Check against gross errors in max range constants
+    EXPECT_LE(SONAR_MAX_RANGE_WITH_TILT, SONAR_MAX_RANGE);
+    EXPECT_LE(SONAR_MAX_RANGE_ACCURACY_HIGH, SONAR_MAX_RANGE);
+}
+