Return status 1 from _file_is_text() when path is blank or nonexi…

…stent.

refs gh-304

nb

@@ -1795,7 +1795,7 @@ _file_is_text() {
                   --exclude=tar             \
                   -b --mime-type)" =~ ^text ]]
         else
-          return 0
+          [[ -f "${_file_path:-}"           ]]
         fi
     }
 }

test/helpers-file-is-text.bats

@@ -0,0 +1,43 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+@test "'_file_is_text()' returns status 0 for text file." {
+  run "${_NB}" helpers file_is_text "${NB_TEST_BASE_PATH}/example.asciidoc"
+
+  printf "\${status}: '%s'\\n" "${status}"
+  printf "\${output}: '%s'\\n" "${output}"
+
+  [[    "${status}"  -eq 0  ]]
+  [[ -z "${output}"         ]]
+}
+
+@test "'_file_is_text()' returns status 1 for pdf file." {
+  run "${_NB}" helpers file_is_text "${NB_TEST_BASE_PATH}/example.pdf"
+
+  printf "\${status}: '%s'\\n" "${status}"
+  printf "\${output}: '%s'\\n" "${output}"
+
+  [[    "${status}"  -eq 1  ]]
+  [[ -z "${output}"         ]]
+}
+
+@test "'_file_is_text()' returns status 1 for nonexistent file." {
+  run "${_NB}" helpers file_is_text "${NB_TEST_BASE_PATH}/nonexistent"
+
+  printf "\${status}: '%s'\\n" "${status}"
+  printf "\${output}: '%s'\\n" "${output}"
+
+  [[    "${status}"  -eq 1  ]]
+  [[ -z "${output}"         ]]
+}
+
+@test "'_file_is_text()' returns status 1 for blank file path." {
+  run "${_NB}" helpers file_is_text ""
+
+  printf "\${status}: '%s'\\n" "${status}"
+  printf "\${output}: '%s'\\n" "${output}"
+
+  [[    "${status}"  -eq 1  ]]
+  [[ -z "${output}"         ]]
+}