Improve reliability of KVStore general tests

In kvstore_init, prior to initializing the kvstore, erase the
underlying block storage device. This ensures that each test run
starts from a consistent state and avoids failures that can result
if a previous test run left the storage in an inconsistent state.

features/storage/TESTS/kvstore/general_tests_phase_1/main.cpp

@@ -78,6 +78,12 @@ static inline uint32_t align_up(uint32_t val, uint32_t size)
 //init the blockdevice
 static void kvstore_init()
 {
+    // This directly corresponds to the pages allocated for each of the SecureStore block devices
+    // For the others it may not match exactly to the space that is used, but it is expected to
+    // be a close enough approximation to act as a guideline for how much of the block device we
+    // need to erase in order to ensure a stable initial condition.
+    const size_t PAGES_ESTIMATE = 40;
+
     int res;
     size_t program_size, erase_size, ul_bd_size, rbp_bd_size;
     BlockDevice *sec_bd;
@@ -85,6 +91,11 @@ static void kvstore_init()
     res = bd->init();
     TEST_ASSERT_EQUAL_ERROR_CODE(0, res);
     int erase_val = bd->get_erase_value();
+    // Clear out any stale data that might be left from a previous test.
+    // Multiply by 2 because SecureStore requires two underlying block devices of this size
+    size_t bytes_to_erase = align_up(2 * PAGES_ESTIMATE * bd->get_program_size(), bd->get_erase_size());
+
+    bd->erase(0, bytes_to_erase);
     res = bd->deinit();
     TEST_ASSERT_EQUAL_ERROR_CODE(0, res);
 
@@ -121,9 +132,8 @@ static void kvstore_init()
         erase_size = sec_bd->get_erase_size();
         // We must be able to hold at least 10 small keys (20 program sectors) and master record + internal data
         // but minimum of 2 erase sectors, so that the garbage collection way work
-        ul_bd_size  = align_up(program_size * 40, erase_size * 2);
+        ul_bd_size  = align_up(program_size * PAGES_ESTIMATE, erase_size * 2);
-        rbp_bd_size = align_up(program_size * 40, erase_size * 2);
+        rbp_bd_size = align_up(program_size * PAGES_ESTIMATE, erase_size * 2);
-
         TEST_ASSERT((ul_bd_size + rbp_bd_size) < sec_bd->size());
 
         res = sec_bd->deinit();

features/storage/TESTS/kvstore/general_tests_phase_2/main.cpp

@@ -78,6 +78,12 @@ static inline uint32_t align_up(uint32_t val, uint32_t size)
 //init the blockdevice
 static void kvstore_init()
 {
+    // This directly corresponds to the pages allocated for each of the SecureStore block devices
+    // For the others it may not match exactly to the space that is used, but it is expected to
+    // be a close enough approximation to act as a guideline for how much of the block device we
+    // need to erase in order to ensure a stable initial condition.
+    const size_t PAGES_ESTIMATE = 40;
+
     int res;
     size_t program_size, erase_size, ul_bd_size, rbp_bd_size;
     BlockDevice *sec_bd;
@@ -85,6 +91,11 @@ static void kvstore_init()
     res = bd->init();
     TEST_ASSERT_EQUAL_ERROR_CODE(0, res);
     int erase_val = bd->get_erase_value();
+    // Clear out any stale data that might be left from a previous test
+    // Multiply by 2 because SecureStore requires two underlying block devices of this size
+    size_t bytes_to_erase = align_up(2 * PAGES_ESTIMATE * bd->get_program_size(), bd->get_erase_size());
+
+    bd->erase(0, bytes_to_erase);
     res = bd->deinit();
     TEST_ASSERT_EQUAL_ERROR_CODE(0, res);
 
@@ -121,8 +132,8 @@ static void kvstore_init()
         erase_size = sec_bd->get_erase_size();
         // We must be able to hold at least 10 small keys (20 program sectors) and master record + internal data
         // but minimum of 2 erase sectors, so that the garbage collection way work
-        ul_bd_size  = align_up(program_size * 40, erase_size * 2);
+        ul_bd_size  = align_up(program_size * PAGES_ESTIMATE, erase_size * 2);
-        rbp_bd_size = align_up(program_size * 40, erase_size * 2);
+        rbp_bd_size = align_up(program_size * PAGES_ESTIMATE, erase_size * 2);
 
         res = sec_bd->deinit();
         TEST_ASSERT_EQUAL_ERROR_CODE(MBED_SUCCESS, res);