diff --git a/include/config.h b/include/config.h
index 6c9e6a4..7e6b21b 100644
--- a/include/config.h
+++ b/include/config.h
@@ -20,6 +20,10 @@ enum ConfigError {
   CE_ENV_ROOT_DIR_INVALID,
   // The target argument is invalid.
   CE_TARGET_INVALID,
+  // No spec with the given name was found.
+  CE_TARGET_NOT_FOUND,
+  // The spec is not a directory.
+  CE_TARGET_NOT_DIR,
 };
 
 enum ConfigError config_load(
diff --git a/main.c b/main.c
index 12c5489..fa1b610 100644
--- a/main.c
+++ b/main.c
@@ -1,3 +1,4 @@
+#include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -7,76 +8,99 @@
 #include "parser.h"
 #include "validator.h"
 
-const char *ENV_BOOTSTRAP_ROOT_DIR = "BOOTSTRAP_ROOT_DIR";
-
-int main(int argc, char **argv) {
-  if (argc != 2) {
-    fprintf(stderr, "Usage: bootstrap <spec>\n");
-    exit(EXIT_FAILURE);
-  }
-
-  int retval = EXIT_SUCCESS;
+static int run(const char *root_dir, const char *target) {
+  int retval = EXIT_FAILURE;
   char *cwd = getcwd(0, 0);
-  const char *root_dir = getenv(ENV_BOOTSTRAP_ROOT_DIR);
-  const char *target = argv[1];
-
-  // `cwd` must be free'd.
+  if (!root_dir) {
+    root_dir = getenv("BOOTSTRAP_ROOT_DIR");
+  }
 
   struct Config *config = 0;
   switch (config_load(cwd, root_dir, target, &config)) {
   case CE_ENV_CWD_INVALID:
-    fprintf(stderr, "Could not retrieve the $CWD value.");
-    retval = EXIT_FAILURE;
-    goto cwd_cleanup;
+    fprintf(stderr, "Could not retrieve $CWD.\n");
+    goto cleanup_cwd;
   case CE_ENV_ROOT_DIR_INVALID:
-    fprintf(stderr, "Must specify $BOOTSTRAP_ROOT_DIR environment variable.");
-    retval = EXIT_FAILURE;
-    goto cwd_cleanup;
+    fprintf(
+      stderr,
+      "Either supply a value to `-d` or specify the $BOOTSTRAP_ROOT_DIR "
+      "environment variable.\n"
+    );
+    goto cleanup_cwd;
   case CE_TARGET_INVALID:
-    fprintf(stderr, "Target spec `%s` is invalid.", argv[1]);
-    retval = EXIT_FAILURE;
-    goto cwd_cleanup;
+    fprintf(stderr, "Spec `%s` is invalid.\n", target);
+    goto cleanup_cwd;
+  case CE_TARGET_NOT_FOUND:
+    fprintf(stderr, "Spec `%s` not found.\n", target);
+    goto cleanup_cwd;
+  case CE_TARGET_NOT_DIR:
+    fprintf(stderr, "Spec `%s` is not a directory.\n", target);
+    goto cleanup_cwd;
   }
 
-  // `config` must be free'd.
-
   cJSON *parsed = 0;
   switch (parse_spec_json(config, &parsed)) {
   case SPE_CANNOT_OPEN:
-    fprintf(stderr, "Found `spec.json` but could not open.");
-    retval = EXIT_FAILURE;
-    goto config_cleanup;
+    fprintf(stderr, "Cannot open `%s/spec.json`.\n", target);
+    goto cleanup_config;
   case SPE_INVALID_SYNTAX:
-    fprintf(stderr, "`spec.json` does not conform to bootstrap format.");
-    retval = EXIT_FAILURE;
-    goto config_cleanup;
+    fprintf(stderr, "`%s/spec.json` is not valid JSON.\n", target);
+    goto cleanup_config;
   }
 
-  // `parsed` must be free'd.
-
   struct DynArray *prompts = 0;
   switch (validate_spec_json(parsed, &prompts)) {
   case SVE_NOT_TOPLEVEL_OBJECT:
-    fprintf(stderr, "`spec.json` top-level JSON value must be object.");
-    retval = EXIT_FAILURE;
-    goto parsed_cleanup;
+    fprintf(stderr, "`%s/spec.json` is not a JSON object.\n", target);
+    goto cleanup_parsed;
   case SVE_INVALID_VALUE:
-    fprintf(stderr, "Encountered unknown `spec.json` value type.");
-    retval = EXIT_FAILURE;
-    goto parsed_cleanup;
+    fprintf(stderr, "unknown value type found in `%s/spec.json`.\n", target);
+    goto cleanup_parsed;
   }
 
   // TODO: Extract the prompts out of the `spec.json` file.
   // TODO: Load in the curses interface.
   // TODO: Run `run.sh`.
 
-parsed_cleanup:
+  retval = EXIT_SUCCESS;
+
+cleanup_parsed:
   cJSON_Delete(parsed);
 
-config_cleanup:
+cleanup_config:
   config_free(config);
 
-cwd_cleanup:
+cleanup_cwd:
   free(cwd);
   return retval;
 }
+
+int main(int argc, char **argv) {
+  char *root_dir = 0;
+  char *target = 0;
+
+  int opt;
+  while ((opt = getopt(argc, argv, "d:")) != -1) {
+    switch (opt) {
+    case 'd':
+      root_dir = optarg;
+      break;
+    }
+  }
+
+  for (int index = optind; index < argc; index++) {
+    if (target == 0) {
+      target = argv[index];
+    } else {
+      fprintf(stderr, "Usage: bootstrap [-d <ROOT_DIR>] <spec>\n");
+      return EXIT_FAILURE;
+    }
+  }
+
+  if (!target) {
+    fprintf(stderr, "Usage: bootstrap [-d <ROOT_DIR>] <spec>\n");
+    return EXIT_FAILURE;
+  }
+
+  return run(root_dir, target);
+}
diff --git a/src/config.c b/src/config.c
index 4db0451..c871689 100644
--- a/src/config.c
+++ b/src/config.c
@@ -1,7 +1,10 @@
+#include <errno.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/stat.h>
 
 #include "config.h"
+#include "path.h"
 
 enum ConfigError config_load(
   const char *cwd,
@@ -19,6 +22,27 @@ enum ConfigError config_load(
     return CE_TARGET_INVALID;
   }
 
+  { // Check if the specified directory exists.
+    struct stat sb;
+
+    const char *segments[] = {root_dir, target};
+    char *filepath =
+      join_path_segments(sizeof(segments) / sizeof(char *), segments);
+
+    int stat_res = stat(filepath, &sb);
+    free(filepath);
+
+    if (stat_res == -1) {
+      if (errno == ENOENT) {
+        return CE_TARGET_NOT_FOUND;
+      }
+      return CE_TARGET_INVALID;
+    }
+    if (!S_ISDIR(sb.st_mode)) {
+      return CE_TARGET_NOT_DIR;
+    }
+  }
+
   *config = malloc(sizeof(struct Config));
   (*config)->cwd = cwd;
   (*config)->root_dir = root_dir;
diff --git a/test/runner.c b/test/runner.c
index 556f3d5..d0f0aa6 100644
--- a/test/runner.c
+++ b/test/runner.c
@@ -9,12 +9,13 @@ int main(int argc, char *argv[]) {
   sput_start_testing();
 
   sput_enter_suite("config");
-  sput_run_test(test_config_load_root_dir_invalid);
-  sput_run_test(test_config_load_target_invalid);
+  sput_run_test(test_config_load_invalid_args);
+  sput_run_test(test_config_load_spec_not_found);
+  sput_run_test(test_config_load_spec_not_dir);
   sput_run_test(test_config_load_success);
 
   sput_enter_suite("dyn_array");
-  sput_run_test(test_dyn_array_empty);
+  sput_run_test(test_dyn_array_zero_capacity);
   sput_run_test(test_dyn_array_nonzero_capacity);
 
   sput_enter_suite("path");
diff --git a/test/specs/not_dir b/test/specs/not_dir
new file mode 100644
index 0000000..e69de29
diff --git a/test/test_config.h b/test/test_config.h
index d726c10..6512a72 100644
--- a/test/test_config.h
+++ b/test/test_config.h
@@ -1,58 +1,94 @@
 #ifndef _BOOTSTRAP_TEST_CONFIG
 #define _BOOTSTRAP_TEST_CONFIG
 
+#include <unistd.h>
+
 #include "config.h"
+#include "path.h"
 #include "sput.h"
 
-static const char *SAMPLE_CWD = "/home/jrpotter/Documents/bootstrap";
-static const char *SAMPLE_ROOT_DIR = "/usr/local/share/specs";
-static const char *SAMPLE_TARGET = "example-target";
+struct TestConfigFixture {
+  char *cwd;
+  char *root_dir;
+  char *target;
+};
+
+static struct TestConfigFixture *test_config_setup() {
+  char *cwd = getcwd(0, 0);
+  const char *segments[] = {cwd, "test", "specs"};
+  char *root_dir =
+    join_path_segments(sizeof(segments) / sizeof(char *), segments);
+
+  struct TestConfigFixture *fixture = malloc(sizeof(struct TestConfigFixture));
+  fixture->cwd = getcwd(0, 0);
+  fixture->root_dir = root_dir;
+  fixture->target = "minimal_spec_json";
+
+  return fixture;
+}
+
+static void test_config_teardown(struct TestConfigFixture *fixture) {
+  free(fixture->cwd);
+  free(fixture->root_dir);
+  free(fixture);
+}
+
+static void test_config_load_invalid_args() {
+  struct TestConfigFixture *fixture = test_config_setup();
 
-/*
-A valid $CWD environment variable value must be supplied.
-*/
-static void test_config_load_cwd_invalid() {
   struct Config *config = 0;
-  enum ConfigError retval =
-      config_load(0, SAMPLE_ROOT_DIR, SAMPLE_TARGET, &config);
+  enum ConfigError retval = 0;
+
+  retval = config_load(0, fixture->root_dir, fixture->target, &config);
   sput_fail_unless(retval == CE_ENV_CWD_INVALID, "target == 0");
-}
-
-/*
-A valid $BOOTSTRAP_ROOT_DIR environment variable value must be supplied.
-*/
-static void test_config_load_root_dir_invalid() {
-  struct Config *config = 0;
-  enum ConfigError retval = config_load(SAMPLE_CWD, 0, SAMPLE_TARGET, &config);
+  retval = config_load(fixture->cwd, 0, fixture->target, &config);
   sput_fail_unless(retval == CE_ENV_ROOT_DIR_INVALID, "root_dir == 0");
-}
-
-/*
-A valid target value must be supplied.
-*/
-static void test_config_load_target_invalid() {
-  struct Config *config = 0;
-  enum ConfigError retval =
-      config_load(SAMPLE_CWD, SAMPLE_ROOT_DIR, 0, &config);
+  retval = config_load(fixture->cwd, fixture->root_dir, 0, &config);
   sput_fail_unless(retval == CE_TARGET_INVALID, "target == 0");
+
+  test_config_teardown(fixture);
 }
 
-/*
-If the supplied arguments to `config_load` are non-NULL, we should be able to
-successfully construct a new @Config instance.
-*/
-static void test_config_load_success() {
+static void test_config_load_spec_not_found() {
+  struct TestConfigFixture *fixture = test_config_setup();
+
   struct Config *config = 0;
   enum ConfigError retval =
-      config_load(SAMPLE_CWD, SAMPLE_ROOT_DIR, SAMPLE_TARGET, &config);
+    config_load(fixture->cwd, fixture->root_dir, "not_found", &config);
+  sput_fail_unless(retval == CE_TARGET_NOT_FOUND, "target not found");
+
+  test_config_teardown(fixture);
+}
+
+static void test_config_load_spec_not_dir() {
+  struct TestConfigFixture *fixture = test_config_setup();
+
+  struct Config *config = 0;
+  enum ConfigError retval =
+    config_load(fixture->cwd, fixture->root_dir, "not_dir", &config);
+  sput_fail_unless(retval == CE_TARGET_NOT_DIR, "target not dir");
+
+  test_config_teardown(fixture);
+}
+
+static void test_config_load_success() {
+  struct TestConfigFixture *fixture = test_config_setup();
+
+  struct Config *config = 0;
+  enum ConfigError retval =
+    config_load(fixture->cwd, fixture->root_dir, fixture->target, &config);
 
   sput_fail_unless(retval == 0, "config_load() success");
-  sput_fail_unless(strcmp(config->root_dir, SAMPLE_ROOT_DIR) == 0,
-                   "config_load() root_dir");
-  sput_fail_unless(strcmp(config->target, SAMPLE_TARGET) == 0,
-                   "config_load() target");
+  sput_fail_unless(strcmp(config->cwd, fixture->cwd) == 0, "config_load() cwd");
+  sput_fail_unless(
+    strcmp(config->root_dir, fixture->root_dir) == 0, "config_load() root_dir"
+  );
+  sput_fail_unless(
+    strcmp(config->target, fixture->target) == 0, "config_load() target"
+  );
 
   config_free(config);
+  test_config_teardown(fixture);
 }
 
 #endif /* _BOOTSTRAP_TEST_CONFIG */
diff --git a/test/test_dyn_array.h b/test/test_dyn_array.h
index 9cdb115..61bb4de 100644
--- a/test/test_dyn_array.h
+++ b/test/test_dyn_array.h
@@ -7,7 +7,7 @@
 /*
 A @DynArray with zero capacity can be instantiated and have entries pushed onto.
 */
-static void test_dyn_array_empty() {
+static void test_dyn_array_zero_capacity() {
   struct DynArray *a = dyn_array_new(0);
   sput_fail_unless(a->size == 0, "a->size == 0");
   sput_fail_unless(a->_capacity == 1, "a->_capacity == 1");
diff --git a/test/test_parser.h b/test/test_parser.h
index f72d4b8..ed32429 100644
--- a/test/test_parser.h
+++ b/test/test_parser.h
@@ -9,76 +9,75 @@
 #include "path.h"
 #include "sput.h"
 
+struct TestParserFixture {
+  char *cwd;
+  char *root_dir;
+  const char *target;
+  struct Config config;
+};
+
+static struct TestParserFixture *test_parser_setup(const char *target) {
+  char *cwd = getcwd(0, 0);
+  const char *segments[] = {cwd, "test", "specs"};
+  char *root_dir =
+    join_path_segments(sizeof(segments) / sizeof(char *), segments);
+
+  struct TestParserFixture *fixture = malloc(sizeof(struct TestParserFixture));
+  fixture->cwd = getcwd(0, 0);
+  fixture->root_dir = root_dir;
+  fixture->target = target;
+
+  // Reproduce in `Config` instance for convenience.
+  fixture->config.cwd = fixture->cwd;
+  fixture->config.root_dir = fixture->root_dir;
+  fixture->config.target = fixture->target;
+
+  return fixture;
+}
+
+static void test_parser_teardown(struct TestParserFixture *fixture) {
+  free(fixture->cwd);
+  free(fixture->root_dir);
+  free(fixture);
+}
+
 /*
 A missing `spec.json` file is not an error. Our parsed @cJSON instance should
 be set to NULL in this case.
 */
 static void test_parse_spec_json_missing() {
-  char *cwd = getcwd(0, 0);
-
-  const char *segments[] = {cwd, "test", "specs"};
-  char *root_dir =
-    join_path_segments(sizeof(segments) / sizeof(char *), segments);
-
-  struct Config config = {
-    cwd,
-    root_dir,
-    "no_spec_json",
-  };
+  struct TestParserFixture *fixture = test_parser_setup("no_spec_json");
 
   cJSON *parsed = 0;
-  enum SpecParseError retval = parse_spec_json(&config, &parsed);
+  enum SpecParseError retval = parse_spec_json(&fixture->config, &parsed);
   sput_fail_unless(retval == 0, "no spec.json, success");
   sput_fail_unless(parsed == 0, "no spec.json, no parsed");
 
-  free(cwd);
-  free(root_dir);
+  test_parser_teardown(fixture);
 }
 
 static void test_parse_spec_json_minimal() {
-  char *cwd = getcwd(0, 0);
-
-  const char *segments[] = {cwd, "test", "specs"};
-  char *root_dir =
-    join_path_segments(sizeof(segments) / sizeof(char *), segments);
-
-  struct Config config = {
-    cwd,
-    root_dir,
-    "minimal_spec_json",
-  };
+  struct TestParserFixture *fixture = test_parser_setup("minimal_spec_json");
 
   cJSON *parsed = 0;
-  enum SpecParseError retval = parse_spec_json(&config, &parsed);
+  enum SpecParseError retval = parse_spec_json(&fixture->config, &parsed);
   sput_fail_unless(retval == 0, "minimal spec.json, success");
   sput_fail_unless(parsed != 0, "minimal spec.json, parsed");
 
-  free(cwd);
-  free(root_dir);
+  test_parser_teardown(fixture);
 }
 
 static void test_parse_spec_json_invalid() {
-  char *cwd = getcwd(0, 0);
-
-  const char *segments[] = {cwd, "test", "specs"};
-  char *root_dir =
-    join_path_segments(sizeof(segments) / sizeof(char *), segments);
-
-  struct Config config = {
-    cwd,
-    root_dir,
-    "invalid_spec_json",
-  };
+  struct TestParserFixture *fixture = test_parser_setup("invalid_spec_json");
 
   cJSON *parsed = 0;
-  enum SpecParseError retval = parse_spec_json(&config, &parsed);
+  enum SpecParseError retval = parse_spec_json(&fixture->config, &parsed);
   sput_fail_unless(
     retval == SPE_INVALID_SYNTAX, "invalid spec.json, INVALID_SYNTAX"
   );
   sput_fail_unless(parsed == 0, "invalid spec.json, not parsed");
 
-  free(cwd);
-  free(root_dir);
+  test_parser_teardown(fixture);
 }
 
 #endif /* _BOOTSTRAP_TEST_PARSER */