From 425aeafedfc00f739fafda250a0f21c6d8e8ec69 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christina=20S=C3=B8rensen?= <christina@cafkafk.com>
Date: Mon, 9 Dec 2024 18:37:41 +0100
Subject: [PATCH] feat(jq): vehicle purchase
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Signed-off-by: Christina Sørensen <christina@cafkafk.com>
---
 jq/vehicle-purchase/.exercism/config.json     |  20 +
 jq/vehicle-purchase/.exercism/metadata.json   |   1 +
 jq/vehicle-purchase/HELP.md                   | 114 ++++
 jq/vehicle-purchase/HINTS.md                  |  26 +
 jq/vehicle-purchase/README.md                 | 238 +++++++
 jq/vehicle-purchase/bats-extra.bash           | 637 ++++++++++++++++++
 jq/vehicle-purchase/bats-jq.bash              |  29 +
 .../test-vehicle-purchase.bats                | 108 +++
 jq/vehicle-purchase/vehicle-purchase.jq       |  27 +
 9 files changed, 1200 insertions(+)
 create mode 100644 jq/vehicle-purchase/.exercism/config.json
 create mode 100644 jq/vehicle-purchase/.exercism/metadata.json
 create mode 100644 jq/vehicle-purchase/HELP.md
 create mode 100644 jq/vehicle-purchase/HINTS.md
 create mode 100644 jq/vehicle-purchase/README.md
 create mode 100644 jq/vehicle-purchase/bats-extra.bash
 create mode 100644 jq/vehicle-purchase/bats-jq.bash
 create mode 100644 jq/vehicle-purchase/test-vehicle-purchase.bats
 create mode 100644 jq/vehicle-purchase/vehicle-purchase.jq

diff --git a/jq/vehicle-purchase/.exercism/config.json b/jq/vehicle-purchase/.exercism/config.json
new file mode 100644
index 0000000..f105538
--- /dev/null
+++ b/jq/vehicle-purchase/.exercism/config.json
@@ -0,0 +1,20 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "vehicle-purchase.jq"
+    ],
+    "test": [
+      "test-vehicle-purchase.bats"
+    ],
+    "exemplar": [
+      ".meta/exemplar.jq"
+    ]
+  },
+  "forked_from": [
+    "javascript/vehicle-purchase"
+  ],
+  "blurb": "Learn about comparison and conditionals while preparing for your next vehicle purchase"
+}
diff --git a/jq/vehicle-purchase/.exercism/metadata.json b/jq/vehicle-purchase/.exercism/metadata.json
new file mode 100644
index 0000000..2b71b9e
--- /dev/null
+++ b/jq/vehicle-purchase/.exercism/metadata.json
@@ -0,0 +1 @@
+{"track":"jq","exercise":"vehicle-purchase","id":"d51f6b81e3894e8285afd1217f4afd39","url":"https://exercism.org/tracks/jq/exercises/vehicle-purchase","handle":"cafkafk","is_requester":true,"auto_approve":false}
\ No newline at end of file
diff --git a/jq/vehicle-purchase/HELP.md b/jq/vehicle-purchase/HELP.md
new file mode 100644
index 0000000..d9135b5
--- /dev/null
+++ b/jq/vehicle-purchase/HELP.md
@@ -0,0 +1,114 @@
+# Help
+
+## Running the tests
+
+Each exercise contains a test file.
+Run the tests using the `bats` program.
+
+```bash
+bats test-hello-world.bats
+```
+
+`bats` will need to be installed.
+See the [Testing on the Bash track][bash] page for instructions to install `bats` for your system.
+
+### bats is implemented in bash
+
+The bats file is a bash script, with some special functions recognized by the `bats` command.
+You'll see some tests that look like
+
+```sh
+jq -f some-exercise.jq <<< "{some,json,here}"
+```
+
+That `<<<` syntax is a bash [Here String][here-string].
+It sends the string on the right-hand side into the standard input of the program on the left-hand side.
+It is ([approximately][so]) the same as
+
+```sh
+echo "{some,json,here}" | jq -f some-exercise.jq
+```
+
+## Help for assert functions
+
+The tests use functions from the [bats-assert][bats-assert] library.
+Help for the various `assert*` functions can be found there.
+
+## Skipped tests
+
+Solving an exercise means making all its tests pass.
+By default, only one test (the first one) is executed when you run the tests.
+This is intentional, as it allows you to focus on just making that one test pass.
+Once it passes, you can enable the next test by commenting out or removing the
+
+    [[ $BATS_RUN_SKIPPED == true ]] || skip
+
+annotations prepending other tests.
+
+## Overriding skips
+
+To run all tests, including the ones with `skip` annotations, you can run:
+
+```bash
+BATS_RUN_SKIPPED=true bats test-some-exercise.bats
+```
+
+It can be convenient to use a wrapper function to save on typing: in `bash` you can do:
+
+```bash
+bats() {
+    BATS_RUN_SKIPPED=true command bats *.bats
+}
+```
+
+Then run tests with just:
+
+```bash
+bats
+```
+
+## Debugging in `jq`
+
+`jq` comes with a handy [`debug`][debug] filter.
+Use it while you are developing your exercise solutions to inspect the data that is currently in the jq pipline.
+See the [debugging doc][debugging] for more details.
+
+
+[bash]: https://exercism.org/docs/tracks/bash/tests
+[bats-assert]: https://github.com/bats-core/bats-assert
+[here-string]: https://www.gnu.org/software/bash/manual/bash.html#Here-Strings
+[so]: https://unix.stackexchange.com/a/80372/4667
+[debug]: https://jqlang.github.io/jq/manual/v1.7/#debug
+[debugging]: https://exercism.org/docs/tracks/jq/debugging
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit vehicle-purchase.jq` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [jq track's documentation](https://exercism.org/docs/tracks/jq)
+- The [jq track's programming category on the forum](https://forum.exercism.org/c/programming/jq)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+## Need more help?
+
+- Go to the [Exercism Community forum](https://forum.exercism.org) to get support and ask questions (or just chat!)
+  - Use the [Exercism Support](https://forum.exercism.org/c/support/8) category if you face any issues with working in the web editor, or downloading or submitting your exercises locally.
+  - Use the [Programming:jq](https://forum.exercism.org/c/programming/jq/133) category for jq-specific topics.
+- Join the community on [Exercism's Discord server](https://exercism.org/r/discord).
+- [StackOverflow](https://stackoverflow.com/questions/tagged/jq) can be used to search for your problem and see if it has been answered already.
+  You can also ask and answer questions.
+- [Github issue tracker](https://github.com/exercism/jq/issues) is where we track our development and maintainance of `jq` exercises in exercism.
+  If none of the above links help you, feel free to post an issue here.
\ No newline at end of file
diff --git a/jq/vehicle-purchase/HINTS.md b/jq/vehicle-purchase/HINTS.md
new file mode 100644
index 0000000..fde389b
--- /dev/null
+++ b/jq/vehicle-purchase/HINTS.md
@@ -0,0 +1,26 @@
+# Hints
+
+## 1. Determine if you will need a drivers license
+
+- Use the [equality operator] to check whether your input equals a certain string.
+- Use one of the two [boolean operators] to combine the two requirements.
+- You do not need an if-statement to solve this task. You can return the boolean expression you build directly.
+
+## 2. Choose between two potential vehicles to buy
+
+- You will need the `if-then-else` [conditional expression] for this task.
+- Use a [comparison operator] to determine which option comes first in dictionary order.
+- Finally, construct the recommendation sentence.
+  You can use the concatenation or string interpolation that you learned in the Strings concept to construct the recommendation sentence.
+
+## 3. Calculate an estimation for the price of a used vehicle
+
+- Start with determining the percentage based on the age of the vehicle.
+  Use an `if-elsif-else` expression.
+- To calculate the result, apply the percentage to the original price.
+  For example, `30% of x` can be calculated by multiplying `x` by `30` and dividing by `100`.
+
+[equality operator]: https://jqlang.github.io/jq/manual/v1.7/#==-!=
+[boolean operators]: https://jqlang.github.io/jq/manual/v1.7/#and-or-not
+[comparison operator]: https://jqlang.github.io/jq/manual/v1.7/#%3E-%3E=-%3C=-%3C
+[conditional expression]: https://jqlang.github.io/jq/manual/v1.7/#if-then-else-end
\ No newline at end of file
diff --git a/jq/vehicle-purchase/README.md b/jq/vehicle-purchase/README.md
new file mode 100644
index 0000000..7774440
--- /dev/null
+++ b/jq/vehicle-purchase/README.md
@@ -0,0 +1,238 @@
+# Vehicle Purchase
+
+Welcome to Vehicle Purchase on Exercism's jq Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
+
+## Introduction
+
+## Compare
+
+### Comparing Numbers
+
+In `jq` numbers can be compared using the following relational and equality operators.
+
+| Comparison             | Operator |
+| ---------------------- | -------- |
+| Greater than           | `a > b`  |
+| Greater than or equals | `a >= b` |
+| Less than              | `a < b`  |
+| Less than or equals    | `a <= b` |
+| Equals                 | `a == b` |
+| Not equals             | `a != b` |
+
+The result of the comparison is always a boolean value, so either `true` or `false`.
+
+```jq
+1 < 3,      # => true
+2 != 2,     # => false
+1 == 1.0    # => true
+            # All numbers are floating-points, so this is different syntax
+            # for the exact same value.
+```
+
+### Comparing Strings
+
+The comparison operators above can also be used to compare strings.
+In that case, a dictionary (lexicographical) order is applied.
+The ordering is _by unicode codepoint value_.
+
+```jq
+"Apple" > "Pear",   # => false
+"a" < "above",      # => true
+"a" == "A"          # => false
+```
+
+You need to be careful when you compare two variables that appear to contain numeric values but are of type string.
+Due to the dictionary order, the result will not be the same as comparing values of type number.
+
+```jq
+10 < 2,     # => false
+"10" < "2"  # => true (because "1" comes before "2")
+```
+
+### "Strict" Equality
+
+The `jq` `==` operator is like Javascript's `===` in the sense that things that "look" the same, but are of different types, are not equal.
+
+```jq
+"3" == 3    # => false
+            # the value on the left has type string,
+            # the value on the right has type number.
+```
+
+### Comparing Arrays
+
+Two arrays are equal if all the corresponding elements are equal.
+
+```jq
+[1, 2, 3] == [1, 2, 3]      # => true
+[1, 2, 3] == [1, 3, 2]      # => false, different order
+[1, 2, 3] == [1, 2, "3"]    # => false, different types
+```
+
+### Comparing Objects
+
+Two objects are equal if they have the same key-value pairs.
+
+```jq
+{name: "Joe", age: 42} == {age: 42, name: "Joe"}                # => true
+{name: "Joe", age: 42} == {age: 42, name: "Jane"}               # => false
+{name: "Joe", age: 42} == {age: "42", name: "Joe"}              # => false
+{name: "Joe", age: 42} == {age: 42, name: "Joe", height: 175}   # => false
+
+# comparisons will drill down as deeply as required
+{a: {b: {c: [1, 2]}}} == {a: {b: {c: [1, 2]}}}                  # => true
+{a: {b: {c: [1, 2]}}} == {a: {b: {c: [1, 2, 3]}}}               # => false
+```
+
+## Conditionals
+
+### If Expression
+
+`jq`'s **conditional expression** is `if A then B else C end`.
+
+`if-then-else` is a filter like all `jq` builtins: it takes an input and produces an output.
+
+If the expression `A` produces a "truthy" value, then the `if` filter evaluates `B`.
+Otherwise it evaluates `C`.
+The input to the `if` filter will be passed to `B` or `C`.
+
+```jq
+42 | if . < 50 then "small" else "big" end      # => "small"
+```
+
+```jq
+5 | if . % 2 == 0 then . / 2 else . * 4 end     # => 20
+```
+
+~~~~exercism/note
+The `else` clause is **optional** in the current `jq` release (version 1.7):
+the following two statements are equivalent.
+
+```jq
+if A then B else . end
+if A then B end
+```
+
+The `else` clause is **mandatory** in the previous v1.6 release. 
+~~~~
+
+### Nested If-Statements
+
+Further conditions can be added with `elif`.
+
+```jq
+42 | if . < 33 then "small"
+     elif . < 66 then "medium"
+     else "big"
+     end
+# => "medium"
+```
+
+Use as many `elif` clauses as you need.
+
+### Truthiness
+
+The only "false" values in `jq` are: `false` and `null`.
+Everything else is "true", even the number zero and the empty string, array and object.
+
+### Boolean Operators
+
+The **boolean operators** `and` and `or` can be used to build complex queries.
+
+```jq
+42 | if . < 33 or . > 66 then "big or small"
+     else "medium"
+     end
+```
+
+To negate, use `not`. This is a **filter** not an operator.
+
+```jq
+42 | if (. < 33 or . > 66 | not) then "medium"
+     else "big or small"
+     end
+```
+
+### Alternative Operator
+
+The **alternative operator** allows you to specify a "default" value if an expression is false or null.
+
+```jq
+A // B
+
+# This is identical to
+if A then A else B end
+```
+
+To demonstrate
+
+```jq
+[3, 5, 18] | add / 2       # => 13
+[]         | add / 2       # => error: null (null) and number (2) cannot be divided
+[]         | add // 0 / 2  # => 0
+```
+
+## Instructions
+
+In this exercise, you will write some code to help you prepare to buy a vehicle.
+
+You have three tasks: determine if you will need to get a license; choose between two vehicles; and estimate the acceptable price for a used vehicle.
+
+## 1. Determine if you will need a drivers license
+
+Some kinds of vehicles require a drivers license to operate them.
+Assume only the kinds `"car"` and `"truck"` require a license; everything else can be operated without a license.
+
+Implement the `needs_license` function that takes the kind of vehicle and returns a boolean indicating whether you need a license for that kind of vehicle.
+
+```jq
+"car" | needs_license
+# => true
+
+"bike" | needs_license
+# => false
+```
+
+## 2. Choose between two potential vehicles to buy
+
+You have evaluated your options of available vehicles.
+You managed to narrow it down to two options but you need help making the final decision.
+Implement the function `choose_vehicle` that takes an array of two vehicles as input and returns a decision, which is the option that comes first in dictionary order.
+
+```jq
+["Wuling Hongguang", "Toyota Corolla"] | choose_vehicle
+# =>  "Toyota Corolla is clearly the better choice."
+
+["Volkswagen Beetle", "Volkswagen Golf"] | choose_vehicle
+# =>  "Volkswagen Beetle is clearly the better choice."
+```
+
+## 3. Calculate an estimation for the price of a used vehicle
+
+Now that you have made your decision, you want to make sure you get a fair price at the dealership.
+Since you are interested in buying a used vehicle, the price depends on how old the vehicle is.
+For a rough estimate, assume if the vehicle is less than 3 years old, it costs 80% of the original price it had when it was brand new.
+If it is more than 10 years old, it costs 50%.
+If the vehicle is at least 3 years old but not older than 10 years, it costs 70% of the original price.
+
+Implement the `resell_price` function that applies this logic using `if`, `elif` and `else`.
+It takes an object holding the original price and the age of the vehicle and returns the estimated price in the dealership.
+
+```jq
+{"original_price": 1000, "age": 1} | resell_price
+# => 800
+
+{"original_price": 1000, "age": 5} | resell_price
+# => 700
+
+{"original_price": 1000, "age": 15} | resell_price
+# => 500
+```
+
+## Source
+
+### Created by
+
+- @glennj
\ No newline at end of file
diff --git a/jq/vehicle-purchase/bats-extra.bash b/jq/vehicle-purchase/bats-extra.bash
new file mode 100644
index 0000000..54d4807
--- /dev/null
+++ b/jq/vehicle-purchase/bats-extra.bash
@@ -0,0 +1,637 @@
+# This is the source code for bats-support and bats-assert, concatenated
+# * https://github.com/bats-core/bats-support
+# * https://github.com/bats-core/bats-assert
+#
+# Comments have been removed to save space. See the git repos for full source code.
+
+############################################################
+#
+# bats-support - Supporting library for Bats test helpers
+#
+# Written in 2016 by Zoltan Tombol <zoltan dot tombol at gmail dot com>
+#
+# To the extent possible under law, the author(s) have dedicated all
+# copyright and related and neighboring rights to this software to the
+# public domain worldwide. This software is distributed without any
+# warranty.
+#
+# You should have received a copy of the CC0 Public Domain Dedication
+# along with this software. If not, see
+# <http://creativecommons.org/publicdomain/zero/1.0/>.
+#
+
+fail() {
+  (( $# == 0 )) && batslib_err || batslib_err "$@"
+  return 1
+}
+
+batslib_is_caller() {
+  local -i is_mode_direct=1
+
+  # Handle options.
+  while (( $# > 0 )); do
+    case "$1" in
+      -i|--indirect) is_mode_direct=0; shift ;;
+      --) shift; break ;;
+      *) break ;;
+    esac
+  done
+
+  # Arguments.
+  local -r func="$1"
+
+  # Check call stack.
+  if (( is_mode_direct )); then
+    [[ $func == "${FUNCNAME[2]}" ]] && return 0
+  else
+    local -i depth
+    for (( depth=2; depth<${#FUNCNAME[@]}; ++depth )); do
+      [[ $func == "${FUNCNAME[$depth]}" ]] && return 0
+    done
+  fi
+
+  return 1
+}
+
+batslib_err() {
+  { if (( $# > 0 )); then
+      echo "$@"
+    else
+      cat -
+    fi
+  } >&2
+}
+
+batslib_count_lines() {
+  local -i n_lines=0
+  local line
+  while IFS='' read -r line || [[ -n $line ]]; do
+    (( ++n_lines ))
+  done < <(printf '%s' "$1")
+  echo "$n_lines"
+}
+
+batslib_is_single_line() {
+  for string in "$@"; do
+    (( $(batslib_count_lines "$string") > 1 )) && return 1
+  done
+  return 0
+}
+
+batslib_get_max_single_line_key_width() {
+  local -i max_len=-1
+  while (( $# != 0 )); do
+    local -i key_len="${#1}"
+    batslib_is_single_line "$2" && (( key_len > max_len )) && max_len="$key_len"
+    shift 2
+  done
+  echo "$max_len"
+}
+
+batslib_print_kv_single() {
+  local -ir col_width="$1"; shift
+  while (( $# != 0 )); do
+    printf '%-*s : %s\n' "$col_width" "$1" "$2"
+    shift 2
+  done
+}
+
+batslib_print_kv_multi() {
+  while (( $# != 0 )); do
+    printf '%s (%d lines):\n' "$1" "$( batslib_count_lines "$2" )"
+    printf '%s\n' "$2"
+    shift 2
+  done
+}
+
+batslib_print_kv_single_or_multi() {
+  local -ir width="$1"; shift
+  local -a pairs=( "$@" )
+
+  local -a values=()
+  local -i i
+  for (( i=1; i < ${#pairs[@]}; i+=2 )); do
+    values+=( "${pairs[$i]}" )
+  done
+
+  if batslib_is_single_line "${values[@]}"; then
+    batslib_print_kv_single "$width" "${pairs[@]}"
+  else
+    local -i i
+    for (( i=1; i < ${#pairs[@]}; i+=2 )); do
+      pairs[$i]="$( batslib_prefix < <(printf '%s' "${pairs[$i]}") )"
+    done
+    batslib_print_kv_multi "${pairs[@]}"
+  fi
+}
+
+batslib_prefix() {
+  local -r prefix="${1:-  }"
+  local line
+  while IFS='' read -r line || [[ -n $line ]]; do
+    printf '%s%s\n' "$prefix" "$line"
+  done
+}
+
+batslib_mark() {
+  local -r symbol="$1"; shift
+  # Sort line numbers.
+  set -- $( sort -nu <<< "$( printf '%d\n' "$@" )" )
+
+  local line
+  local -i idx=0
+  while IFS='' read -r line || [[ -n $line ]]; do
+    if (( ${1:--1} == idx )); then
+      printf '%s\n' "${symbol}${line:${#symbol}}"
+      shift
+    else
+      printf '%s\n' "$line"
+    fi
+    (( ++idx ))
+  done
+}
+
+batslib_decorate() {
+  echo
+  echo "-- $1 --"
+  cat -
+  echo '--'
+  echo
+}
+
+############################################################
+
+assert() {
+  if ! "$@"; then
+    batslib_print_kv_single 10 'expression' "$*" \
+    | batslib_decorate 'assertion failed' \
+    | fail
+  fi
+}
+
+assert_equal() {
+  if [[ $1 != "$2" ]]; then
+    batslib_print_kv_single_or_multi 8 \
+    'expected' "$2" \
+    'actual'   "$1" \
+    | batslib_decorate 'values do not equal' \
+    | fail
+  fi
+}
+
+assert_failure() {
+  : "${output?}"
+  : "${status?}"
+
+  (( $# > 0 )) && local -r expected="$1"
+  if (( status == 0 )); then
+    batslib_print_kv_single_or_multi 6 'output' "$output" \
+    | batslib_decorate 'command succeeded, but it was expected to fail' \
+    | fail
+  elif (( $# > 0 )) && (( status != expected )); then
+    { local -ir width=8
+      batslib_print_kv_single "$width" \
+      'expected' "$expected" \
+      'actual'   "$status"
+      batslib_print_kv_single_or_multi "$width" \
+      'output' "$output"
+    } \
+    | batslib_decorate 'command failed as expected, but status differs' \
+    | fail
+  fi
+}
+
+assert_line() {
+  local -i is_match_line=0
+  local -i is_mode_partial=0
+  local -i is_mode_regexp=0
+  : "${lines?}"
+
+  # Handle options.
+  while (( $# > 0 )); do
+    case "$1" in
+    -n|--index)
+      if (( $# < 2 )) || ! [[ $2 =~ ^([0-9]|[1-9][0-9]+)$ ]]; then
+        echo "\`--index' requires an integer argument: \`$2'" \
+        | batslib_decorate 'ERROR: assert_line' \
+        | fail
+        return $?
+      fi
+      is_match_line=1
+      local -ri idx="$2"
+      shift 2
+      ;;
+    -p|--partial) is_mode_partial=1; shift ;;
+    -e|--regexp) is_mode_regexp=1; shift ;;
+    --) shift; break ;;
+    *) break ;;
+    esac
+  done
+
+  if (( is_mode_partial )) && (( is_mode_regexp )); then
+    echo "\`--partial' and \`--regexp' are mutually exclusive" \
+    | batslib_decorate 'ERROR: assert_line' \
+    | fail
+    return $?
+  fi
+
+  # Arguments.
+  local -r expected="$1"
+
+  if (( is_mode_regexp == 1 )) && [[ '' =~ $expected ]] || (( $? == 2 )); then
+    echo "Invalid extended regular expression: \`$expected'" \
+    | batslib_decorate 'ERROR: assert_line' \
+    | fail
+    return $?
+  fi
+
+  # Matching.
+  if (( is_match_line )); then
+    # Specific line.
+    if (( is_mode_regexp )); then
+      if ! [[ ${lines[$idx]} =~ $expected ]]; then
+        batslib_print_kv_single 6 \
+        'index' "$idx" \
+        'regexp' "$expected" \
+        'line'  "${lines[$idx]}" \
+        | batslib_decorate 'regular expression does not match line' \
+        | fail
+      fi
+    elif (( is_mode_partial )); then
+      if [[ ${lines[$idx]} != *"$expected"* ]]; then
+        batslib_print_kv_single 9 \
+        'index'     "$idx" \
+        'substring' "$expected" \
+        'line'      "${lines[$idx]}" \
+        | batslib_decorate 'line does not contain substring' \
+        | fail
+      fi
+    else
+      if [[ ${lines[$idx]} != "$expected" ]]; then
+        batslib_print_kv_single 8 \
+        'index'    "$idx" \
+        'expected' "$expected" \
+        'actual'   "${lines[$idx]}" \
+        | batslib_decorate 'line differs' \
+        | fail
+      fi
+    fi
+  else
+    # Contained in output.
+    if (( is_mode_regexp )); then
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        [[ ${lines[$idx]} =~ $expected ]] && return 0
+      done
+      { local -ar single=( 'regexp' "$expected" )
+        local -ar may_be_multi=( 'output' "$output" )
+        local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+        batslib_print_kv_single "$width" "${single[@]}"
+        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
+      } \
+      | batslib_decorate 'no output line matches regular expression' \
+      | fail
+    elif (( is_mode_partial )); then
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        [[ ${lines[$idx]} == *"$expected"* ]] && return 0
+      done
+      { local -ar single=( 'substring' "$expected" )
+        local -ar may_be_multi=( 'output' "$output" )
+        local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+        batslib_print_kv_single "$width" "${single[@]}"
+        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
+      } \
+      | batslib_decorate 'no output line contains substring' \
+      | fail
+    else
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        [[ ${lines[$idx]} == "$expected" ]] && return 0
+      done
+      { local -ar single=( 'line' "$expected" )
+        local -ar may_be_multi=( 'output' "$output" )
+        local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+        batslib_print_kv_single "$width" "${single[@]}"
+        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
+      } \
+      | batslib_decorate 'output does not contain line' \
+      | fail
+    fi
+  fi
+}
+
+assert_output() {
+  local -i is_mode_partial=0
+  local -i is_mode_regexp=0
+  local -i is_mode_nonempty=0
+  local -i use_stdin=0
+  : "${output?}"
+
+  # Handle options.
+  if (( $# == 0 )); then
+    is_mode_nonempty=1
+  fi
+
+  while (( $# > 0 )); do
+    case "$1" in
+    -p|--partial) is_mode_partial=1; shift ;;
+    -e|--regexp) is_mode_regexp=1; shift ;;
+    -|--stdin) use_stdin=1; shift ;;
+    --) shift; break ;;
+    *) break ;;
+    esac
+  done
+
+  if (( is_mode_partial )) && (( is_mode_regexp )); then
+    echo "\`--partial' and \`--regexp' are mutually exclusive" \
+    | batslib_decorate 'ERROR: assert_output' \
+    | fail
+    return $?
+  fi
+
+  # Arguments.
+  local expected
+  if (( use_stdin )); then
+    expected="$(cat -)"
+  else
+    expected="${1-}"
+  fi
+
+  # Matching.
+  if (( is_mode_nonempty )); then
+    if [ -z "$output" ]; then
+      echo 'expected non-empty output, but output was empty' \
+      | batslib_decorate 'no output' \
+      | fail
+    fi
+  elif (( is_mode_regexp )); then
+    if [[ '' =~ $expected ]] || (( $? == 2 )); then
+      echo "Invalid extended regular expression: \`$expected'" \
+      | batslib_decorate 'ERROR: assert_output' \
+      | fail
+    elif ! [[ $output =~ $expected ]]; then
+      batslib_print_kv_single_or_multi 6 \
+      'regexp'  "$expected" \
+      'output' "$output" \
+      | batslib_decorate 'regular expression does not match output' \
+      | fail
+    fi
+  elif (( is_mode_partial )); then
+    if [[ $output != *"$expected"* ]]; then
+      batslib_print_kv_single_or_multi 9 \
+      'substring' "$expected" \
+      'output'    "$output" \
+      | batslib_decorate 'output does not contain substring' \
+      | fail
+    fi
+  else
+    if [[ $output != "$expected" ]]; then
+      batslib_print_kv_single_or_multi 8 \
+      'expected' "$expected" \
+      'actual'   "$output" \
+      | batslib_decorate 'output differs' \
+      | fail
+    fi
+  fi
+}
+
+assert_success() {
+  : "${output?}"
+  : "${status?}"
+
+  if (( status != 0 )); then
+    { local -ir width=6
+      batslib_print_kv_single "$width" 'status' "$status"
+      batslib_print_kv_single_or_multi "$width" 'output' "$output"
+    } \
+    | batslib_decorate 'command failed' \
+    | fail
+  fi
+}
+
+refute() {
+  if "$@"; then
+    batslib_print_kv_single 10 'expression' "$*" \
+    | batslib_decorate 'assertion succeeded, but it was expected to fail' \
+    | fail
+  fi
+}
+
+refute_line() {
+  local -i is_match_line=0
+  local -i is_mode_partial=0
+  local -i is_mode_regexp=0
+  : "${lines?}"
+
+  # Handle options.
+  while (( $# > 0 )); do
+    case "$1" in
+    -n|--index)
+      if (( $# < 2 )) || ! [[ $2 =~ ^([0-9]|[1-9][0-9]+)$ ]]; then
+        echo "\`--index' requires an integer argument: \`$2'" \
+        | batslib_decorate 'ERROR: refute_line' \
+        | fail
+        return $?
+      fi
+      is_match_line=1
+      local -ri idx="$2"
+      shift 2
+      ;;
+    -p|--partial) is_mode_partial=1; shift ;;
+    -e|--regexp) is_mode_regexp=1; shift ;;
+    --) shift; break ;;
+    *) break ;;
+    esac
+  done
+
+  if (( is_mode_partial )) && (( is_mode_regexp )); then
+    echo "\`--partial' and \`--regexp' are mutually exclusive" \
+    | batslib_decorate 'ERROR: refute_line' \
+    | fail
+    return $?
+  fi
+
+  # Arguments.
+  local -r unexpected="$1"
+
+  if (( is_mode_regexp == 1 )) && [[ '' =~ $unexpected ]] || (( $? == 2 )); then
+    echo "Invalid extended regular expression: \`$unexpected'" \
+    | batslib_decorate 'ERROR: refute_line' \
+    | fail
+    return $?
+  fi
+
+  # Matching.
+  if (( is_match_line )); then
+    # Specific line.
+    if (( is_mode_regexp )); then
+      if [[ ${lines[$idx]} =~ $unexpected ]]; then
+        batslib_print_kv_single 6 \
+        'index' "$idx" \
+        'regexp' "$unexpected" \
+        'line'  "${lines[$idx]}" \
+        | batslib_decorate 'regular expression should not match line' \
+        | fail
+      fi
+    elif (( is_mode_partial )); then
+      if [[ ${lines[$idx]} == *"$unexpected"* ]]; then
+        batslib_print_kv_single 9 \
+        'index'     "$idx" \
+        'substring' "$unexpected" \
+        'line'      "${lines[$idx]}" \
+        | batslib_decorate 'line should not contain substring' \
+        | fail
+      fi
+    else
+      if [[ ${lines[$idx]} == "$unexpected" ]]; then
+        batslib_print_kv_single 5 \
+        'index' "$idx" \
+        'line'  "${lines[$idx]}" \
+        | batslib_decorate 'line should differ' \
+        | fail
+      fi
+    fi
+  else
+    # Line contained in output.
+    if (( is_mode_regexp )); then
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        if [[ ${lines[$idx]} =~ $unexpected ]]; then
+          { local -ar single=( 'regexp' "$unexpected" 'index' "$idx" )
+            local -a may_be_multi=( 'output' "$output" )
+            local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+            batslib_print_kv_single "$width" "${single[@]}"
+            if batslib_is_single_line "${may_be_multi[1]}"; then
+              batslib_print_kv_single "$width" "${may_be_multi[@]}"
+            else
+              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" | batslib_prefix | batslib_mark '>' "$idx" )"
+              batslib_print_kv_multi "${may_be_multi[@]}"
+            fi
+          } \
+          | batslib_decorate 'no line should match the regular expression' \
+          | fail
+          return $?
+        fi
+      done
+    elif (( is_mode_partial )); then
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        if [[ ${lines[$idx]} == *"$unexpected"* ]]; then
+          { local -ar single=( 'substring' "$unexpected" 'index' "$idx" )
+            local -a may_be_multi=( 'output' "$output" )
+            local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+            batslib_print_kv_single "$width" "${single[@]}"
+            if batslib_is_single_line "${may_be_multi[1]}"; then
+              batslib_print_kv_single "$width" "${may_be_multi[@]}"
+            else
+              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" | batslib_prefix | batslib_mark '>' "$idx" )"
+              batslib_print_kv_multi "${may_be_multi[@]}"
+            fi
+          } \
+          | batslib_decorate 'no line should contain substring' \
+          | fail
+          return $?
+        fi
+      done
+    else
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        if [[ ${lines[$idx]} == "$unexpected" ]]; then
+          { local -ar single=( 'line' "$unexpected" 'index' "$idx" )
+            local -a may_be_multi=( 'output' "$output" )
+            local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+            batslib_print_kv_single "$width" "${single[@]}"
+            if batslib_is_single_line "${may_be_multi[1]}"; then
+              batslib_print_kv_single "$width" "${may_be_multi[@]}"
+            else
+              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" | batslib_prefix | batslib_mark '>' "$idx" )"
+              batslib_print_kv_multi "${may_be_multi[@]}"
+            fi
+          } \
+          | batslib_decorate 'line should not be in output' \
+          | fail
+          return $?
+        fi
+      done
+    fi
+  fi
+}
+
+refute_output() {
+  local -i is_mode_partial=0
+  local -i is_mode_regexp=0
+  local -i is_mode_empty=0
+  local -i use_stdin=0
+  : "${output?}"
+
+  # Handle options.
+  if (( $# == 0 )); then
+    is_mode_empty=1
+  fi
+
+  while (( $# > 0 )); do
+    case "$1" in
+    -p|--partial) is_mode_partial=1; shift ;;
+    -e|--regexp) is_mode_regexp=1; shift ;;
+    -|--stdin) use_stdin=1; shift ;;
+    --) shift; break ;;
+    *) break ;;
+    esac
+  done
+
+  if (( is_mode_partial )) && (( is_mode_regexp )); then
+    echo "\`--partial' and \`--regexp' are mutually exclusive" \
+    | batslib_decorate 'ERROR: refute_output' \
+    | fail
+    return $?
+  fi
+
+  # Arguments.
+  local unexpected
+  if (( use_stdin )); then
+    unexpected="$(cat -)"
+  else
+    unexpected="${1-}"
+  fi
+
+  if (( is_mode_regexp == 1 )) && [[ '' =~ $unexpected ]] || (( $? == 2 )); then
+    echo "Invalid extended regular expression: \`$unexpected'" \
+    | batslib_decorate 'ERROR: refute_output' \
+    | fail
+    return $?
+  fi
+
+  # Matching.
+  if (( is_mode_empty )); then
+    if [ -n "$output" ]; then
+      batslib_print_kv_single_or_multi 6 \
+      'output' "$output" \
+      | batslib_decorate 'output non-empty, but expected no output' \
+      | fail
+    fi
+  elif (( is_mode_regexp )); then
+    if [[ $output =~ $unexpected ]]; then
+      batslib_print_kv_single_or_multi 6 \
+      'regexp'  "$unexpected" \
+      'output' "$output" \
+      | batslib_decorate 'regular expression should not match output' \
+      | fail
+    fi
+  elif (( is_mode_partial )); then
+    if [[ $output == *"$unexpected"* ]]; then
+      batslib_print_kv_single_or_multi 9 \
+      'substring' "$unexpected" \
+      'output'    "$output" \
+      | batslib_decorate 'output should not contain substring' \
+      | fail
+    fi
+  else
+    if [[ $output == "$unexpected" ]]; then
+      batslib_print_kv_single_or_multi 6 \
+      'output' "$output" \
+      | batslib_decorate 'output equals, but it was expected to differ' \
+      | fail
+    fi
+  fi
+}
diff --git a/jq/vehicle-purchase/bats-jq.bash b/jq/vehicle-purchase/bats-jq.bash
new file mode 100644
index 0000000..3f55da5
--- /dev/null
+++ b/jq/vehicle-purchase/bats-jq.bash
@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+#
+# `bats-core` will consume both stdout and stderr for the `run` command's output.
+# However `jq` prints its DEBUG output on stderr.
+#
+# Lines starting with `["DEBUG:",` will be prefixed with a hash and printed on file descriptor 3.
+# Other lines on stderr will remain on stderr for bats to consume.
+#
+# See `bats-core` docs:
+# - "Printing to the terminal", https://bats-core.readthedocs.io/en/stable/writing-tests.html#printing-to-the-terminal
+# - "File descriptor 3", https://bats-core.readthedocs.io/en/stable/writing-tests.html#file-descriptor-3-read-this-if-bats-hangs
+
+
+jq() {
+    local output stderr rc line
+    stderr=$(mktemp)
+    output=$(command jq "$@" 2> "$stderr")
+    rc=$?
+    while IFS= read -r line || [[ -n $line ]]; do
+        if [[ $line == '["DEBUG:",'* ]]; then
+            echo "# $line" >&3
+        else
+            echo "$line" >&2
+        fi
+    done < "$stderr"
+    rm -f "$stderr"
+    echo "$output"
+    return "$rc"
+}
diff --git a/jq/vehicle-purchase/test-vehicle-purchase.bats b/jq/vehicle-purchase/test-vehicle-purchase.bats
new file mode 100644
index 0000000..162d7bc
--- /dev/null
+++ b/jq/vehicle-purchase/test-vehicle-purchase.bats
@@ -0,0 +1,108 @@
+#!/usr/bin/env bats
+load bats-extra
+load bats-jq
+
+@test requires_a_license_for_a_car {
+    ## task 1
+    run jq -R 'include "vehicle-purchase"; needs_license' <<< 'car'
+    assert_success
+    assert_output "true"
+}
+
+@test requires_a_license_for_a_truck {
+    ## task 1
+    run jq -R 'include "vehicle-purchase"; needs_license' <<< 'truck'
+    assert_success
+    assert_output "true"
+}
+
+@test does_not_require_a_license_for_a_bike {
+    ## task 1
+    run jq -R 'include "vehicle-purchase"; needs_license' <<< 'bike'
+    assert_success
+    assert_output "false"
+}
+
+@test does_not_require_a_license_for_a_stroller {
+    ## task 1
+    run jq -R 'include "vehicle-purchase"; needs_license' <<< 'stroller'
+    assert_success
+    assert_output "false"
+}
+
+@test does_not_require_a_license_for_an_e-scooter {
+    ## task 1
+    run jq -R 'include "vehicle-purchase"; needs_license' <<< 'e-scooter'
+    assert_success
+    assert_output "false"
+}
+
+
+@test correctly_recommends_the_first_option {
+    ## task 2
+    run jq -r 'include "vehicle-purchase"; choose_vehicle' << END_INPUT
+        ["Bugatti Veyron", "Ford Pinto"]
+        ["Chery EQ", "Kia Niro Elektro"]
+END_INPUT
+    assert_success
+    assert_line --index 0 'Bugatti Veyron is clearly the better choice.'
+    assert_line --index 1 'Chery EQ is clearly the better choice.'
+}
+
+@test correctly_recommends_the_second_option {
+    ## task 2
+    run jq -r 'include "vehicle-purchase"; choose_vehicle' << END_INPUT
+        ["Ford Pinto", "Bugatti Veyron"]
+        ["2020 Gazelle Medeo", "2018 Bergamont City"]
+END_INPUT
+    assert_success
+    assert_line --index 0 'Bugatti Veyron is clearly the better choice.'
+    assert_line --index 1 '2018 Bergamont City is clearly the better choice.'
+}
+
+@test price_is_reduced_to_80%_for_age_below_3 {
+    ## task 3
+    run jq 'include "vehicle-purchase"; resell_price' << END_INPUT
+        {"original_price": 40000, "age": 2}
+        {"original_price": 40000, "age": 2.5}
+END_INPUT
+    assert_success
+    assert_line --index 0 '32000'
+    assert_line --index 1 '32000'
+}
+
+@test price_is_reduced_to_50%_for_age_above_10 {
+    ## task 3
+    run jq 'include "vehicle-purchase"; resell_price' << END_INPUT
+        {"original_price": 40000, "age": 12}
+END_INPUT
+    assert_success
+    assert_output '20000'
+}
+
+@test price_is_reduced_to_70%_for_between_3_and_10 {
+    ## task 3
+    run jq 'include "vehicle-purchase"; resell_price' << END_INPUT
+        {"original_price": 25000, "age": 7}
+END_INPUT
+    assert_success
+    assert_output '17500'
+}
+
+@test works_correctly_for_threshold_age_3 {
+    ## task 3
+    run jq 'include "vehicle-purchase"; resell_price' << END_INPUT
+        {"original_price": 40000, "age": 3}
+END_INPUT
+    assert_success
+    assert_output '28000'
+}
+
+@test works_correctly_for_threshold_age_10 {
+    ## task 3
+    run jq 'include "vehicle-purchase"; resell_price' << END_INPUT
+        {"original_price": 25000, "age": 10}
+END_INPUT
+    assert_success
+    assert_output '17500'
+}
diff --git a/jq/vehicle-purchase/vehicle-purchase.jq b/jq/vehicle-purchase/vehicle-purchase.jq
new file mode 100644
index 0000000..258cc99
--- /dev/null
+++ b/jq/vehicle-purchase/vehicle-purchase.jq
@@ -0,0 +1,27 @@
+# Task 1
+# Determines whether or not you need a license to operate a certain kind of vehicle.
+#
+# input: {string} kind of vehicle
+# output: {boolean} whether a license is required
+
+def needs_license: . == "car" or . == "truck";
+
+# Task 2
+# Helps choosing between two options by recommending the one that
+# comes first in dictionary order.
+#
+# input: {array of strings} options to consider
+# output: {string} a sentence of advice which option to choose
+def choose_vehicle: if .[0] < .[1] then .[0] else .[1] end|"\(.) is clearly the better choice.";
+
+# Task 3
+# Calculates an estimate for the price of a used vehicle in the dealership
+# based on the original price and the age of the vehicle.
+#
+# input: {object} with keys "original_price" and "age"
+# output: {number} expected resell price in the dealership
+
+def resell_price:
+  if .age > 10 then  .original_price * 0.5
+  elif .age >= 3 then .original_price * 0.7
+  else .original_price * 0.8 end;