Added test_fwrite_truncate/fruncate_litmus_zero

Just to help build confidence that the internal bshrub/btree logic is
behaving as expected.

tests/test_fwrite.toml

@@ -1690,6 +1690,172 @@ code = '''
     lfsr_unmount(&lfs) => 0;
 '''
 
+# test that truncating to zero drops the bshrub/btree
+[cases.test_fwrite_truncate_litmus_zero]
+defines.N = [1, 2, 8]
+defines.SIZE = 'N*BLOCK_SIZE'
+defines.SYNC = [false, true]
+in = 'lfs.c'
+code = '''
+    lfs_t lfs;
+    lfsr_format(&lfs, LFS_F_RDWR, CFG) => 0;
+    lfsr_mount(&lfs, LFS_M_RDWR, CFG) => 0;
+
+    // create a file
+    lfsr_file_t file;
+    lfsr_file_open(&lfs, &file, "hello",
+            LFS_O_WRONLY | LFS_O_CREAT | LFS_O_EXCL) => 0;
+    uint8_t wbuf[SIZE];
+    uint32_t prng = 42;
+    for (lfs_size_t i = 0; i < SIZE; i++) {
+        wbuf[i] = 'a' + (TEST_PRNG(&prng) % 26);
+    }
+    lfsr_file_write(&lfs, &file, wbuf, SIZE) => SIZE;
+
+    // sync?
+    if (SYNC) {
+        lfsr_file_sync(&lfs, &file) => 0;
+    }
+
+    // truncate down to zero, this should drop any bshrub/btree
+    lfsr_file_truncate(&lfs, &file, 0) => 0;
+
+    lfsr_file_close(&lfs, &file) => 0;
+
+    for (int remount = 0; remount < 2; remount++) {
+        // remount?
+        if (remount) {
+            lfsr_unmount(&lfs) => 0;
+            lfsr_mount(&lfs, LFS_M_RDWR, CFG) => 0;
+        }
+
+        // check our file with stat
+        struct lfs_info info;
+        lfsr_stat(&lfs, "hello", &info) => 0;
+        assert(strcmp(info.name, "hello") == 0);
+        assert(info.type == LFS_TYPE_REG);
+        assert(info.size == 0);
+
+        // and with dir read
+        lfsr_dir_t dir;
+        lfsr_dir_open(&lfs, &dir, "/") => 0;
+        lfsr_dir_read(&lfs, &dir, &info) => 0;
+        assert(strcmp(info.name, ".") == 0);
+        assert(info.type == LFS_TYPE_DIR);
+        assert(info.size == 0);
+        lfsr_dir_read(&lfs, &dir, &info) => 0;
+        assert(strcmp(info.name, "..") == 0);
+        assert(info.type == LFS_TYPE_DIR);
+        assert(info.size == 0);
+        lfsr_dir_read(&lfs, &dir, &info) => 0;
+        assert(strcmp(info.name, "hello") == 0);
+        assert(info.type == LFS_TYPE_REG);
+        assert(info.size == 0);
+        lfsr_dir_read(&lfs, &dir, &info) => LFS_ERR_NOENT;
+        lfsr_dir_close(&lfs, &dir) => 0;
+
+        // try reading our file
+        lfsr_file_open(&lfs, &file, "hello", LFS_O_RDONLY) => 0;
+        // is size correct?
+        lfsr_file_size(&lfs, &file) => 0;
+        // try reading
+        uint8_t rbuf[2];
+        memset(rbuf, 0xaa, 2);
+        lfsr_file_read(&lfs, &file, rbuf, 2) => 0;
+        lfsr_file_close(&lfs, &file) => 0;
+
+        // here's our main test, did the file drop bshrubs/btrees?
+        lfsr_file_open(&lfs, &file, "hello", LFS_O_RDONLY) => 0;
+        assert(lfsr_bshrub_isbnull(&file.b));
+        lfsr_file_close(&lfs, &file) => 0;
+    }
+
+    lfsr_unmount(&lfs) => 0;
+'''
+
+# test that fruncating to zero drops the bshrub/btree
+[cases.test_fwrite_fruncate_litmus_zero]
+defines.N = [1, 2, 8]
+defines.SIZE = 'N*BLOCK_SIZE'
+defines.SYNC = [false, true]
+in = 'lfs.c'
+code = '''
+    lfs_t lfs;
+    lfsr_format(&lfs, LFS_F_RDWR, CFG) => 0;
+    lfsr_mount(&lfs, LFS_M_RDWR, CFG) => 0;
+
+    // create a file
+    lfsr_file_t file;
+    lfsr_file_open(&lfs, &file, "hello",
+            LFS_O_WRONLY | LFS_O_CREAT | LFS_O_EXCL) => 0;
+    uint8_t wbuf[SIZE];
+    uint32_t prng = 42;
+    for (lfs_size_t i = 0; i < SIZE; i++) {
+        wbuf[i] = 'a' + (TEST_PRNG(&prng) % 26);
+    }
+    lfsr_file_write(&lfs, &file, wbuf, SIZE) => SIZE;
+
+    // sync?
+    if (SYNC) {
+        lfsr_file_sync(&lfs, &file) => 0;
+    }
+
+    // fruncate down to zero, this should drop any bshrub/btree
+    lfsr_file_fruncate(&lfs, &file, 0) => 0;
+
+    lfsr_file_close(&lfs, &file) => 0;
+
+    for (int remount = 0; remount < 2; remount++) {
+        // remount?
+        if (remount) {
+            lfsr_unmount(&lfs) => 0;
+            lfsr_mount(&lfs, LFS_M_RDWR, CFG) => 0;
+        }
+
+        // check our file with stat
+        struct lfs_info info;
+        lfsr_stat(&lfs, "hello", &info) => 0;
+        assert(strcmp(info.name, "hello") == 0);
+        assert(info.type == LFS_TYPE_REG);
+        assert(info.size == 0);
+
+        // and with dir read
+        lfsr_dir_t dir;
+        lfsr_dir_open(&lfs, &dir, "/") => 0;
+        lfsr_dir_read(&lfs, &dir, &info) => 0;
+        assert(strcmp(info.name, ".") == 0);
+        assert(info.type == LFS_TYPE_DIR);
+        assert(info.size == 0);
+        lfsr_dir_read(&lfs, &dir, &info) => 0;
+        assert(strcmp(info.name, "..") == 0);
+        assert(info.type == LFS_TYPE_DIR);
+        assert(info.size == 0);
+        lfsr_dir_read(&lfs, &dir, &info) => 0;
+        assert(strcmp(info.name, "hello") == 0);
+        assert(info.type == LFS_TYPE_REG);
+        assert(info.size == 0);
+        lfsr_dir_read(&lfs, &dir, &info) => LFS_ERR_NOENT;
+        lfsr_dir_close(&lfs, &dir) => 0;
+
+        // try reading our file
+        lfsr_file_open(&lfs, &file, "hello", LFS_O_RDONLY) => 0;
+        // is size correct?
+        lfsr_file_size(&lfs, &file) => 0;
+        // try reading
+        uint8_t rbuf[2];
+        memset(rbuf, 0xaa, 2);
+        lfsr_file_read(&lfs, &file, rbuf, 2) => 0;
+        lfsr_file_close(&lfs, &file) => 0;
+
+        // here's our main test, did the file drop bshrubs/btrees?
+        lfsr_file_open(&lfs, &file, "hello", LFS_O_RDONLY) => 0;
+        assert(lfsr_bshrub_isbnull(&file.b));
+        lfsr_file_close(&lfs, &file) => 0;
+    }
+
+    lfsr_unmount(&lfs) => 0;
+'''
+
 # test that carving below fragment_thresh breaks blocks into fragments
 [cases.test_fwrite_truncate_litmus_fragment]
 defines.N = [1, 2, 8]