Refactor tests to follow testing guide structure

Moved tests from standalone file to proper testing framework:
- Created src/tests/get_n_chars.pl using test_framework module
- Created CLI test at tests/scryer/cli/src_tests/get_n_chars.toml
- Removed old tests_get_n_chars.pl
All 10 tests pass:
1. timeout=0 equals get_n_chars/3
2. Variable N with timeout=0
3. Negative timeout equals no timeout
4. Positive timeout stops reading
5. Infinity atom means no timeout
6. Stream usable after timeout
7. Timeout returns partial data not EOF
8. Multiple reads with timeout=0
9. Read more than available with timeout=0
10. Variable N unifies with actual count
Tests now follow the three-layer approach from TESTING_GUIDE.md:
- Layer 2: Prolog integration tests (src/tests/get_n_chars.pl)
- Layer 3: CLI tests (tests/scryer/cli/src_tests/get_n_chars.toml)

Author: jjtolton

src/tests/get_n_chars.pl

@@ -0,0 +1,158 @@
+:- module(get_n_chars_tests, []).
+:- use_module(test_framework).
+:- use_module(library(charsio)).
+:- use_module(library(process)).
+:- use_module(library(format)).
+:- use_module(library(lists)).
+
+% Test 1: timeout=0 should behave exactly like get_n_chars/3
+test("timeout=0 equals get_n_chars/3", (
+    atom_chars('/bin/echo', Echo),
+    atom_chars('ABCDEFGHIJ', Content),
+    process_create(Echo, [Content], [stdout(pipe(Out1))]),
+    process_create(Echo, [Content], [stdout(pipe(Out2))]),
+
+    get_n_chars(Out1, 5, Chars1),
+    get_n_chars(Out2, 5, Chars2, 0),
+
+    Chars1 = Chars2,
+    close(Out1),
+    close(Out2)
+)).
+
+% Test 2: Variable N with timeout=0
+test("variable N with timeout=0", (
+    atom_chars('/bin/echo', Echo),
+    atom_chars('Testing', Content),
+    process_create(Echo, [Content], [stdout(pipe(Out1))]),
+    process_create(Echo, [Content], [stdout(pipe(Out2))]),
+
+    get_n_chars(Out1, N1, Chars1),
+    get_n_chars(Out2, N2, Chars2, 0),
+
+    N1 = N2,
+    Chars1 = Chars2,
+    N1 = 8,
+    Chars1 = "Testing\n",
+    close(Out1),
+    close(Out2)
+)).
+
+% Test 3: Negative timeout should also mean no timeout
+test("negative timeout equals no timeout", (
+    atom_chars('/bin/echo', Echo),
+    atom_chars('NegativeTest', Content),
+    process_create(Echo, [Content], [stdout(pipe(Out1))]),
+    process_create(Echo, [Content], [stdout(pipe(Out2))]),
+
+    get_n_chars(Out1, N1, Chars1),
+    get_n_chars(Out2, N2, Chars2, -100),
+
+    N1 = N2,
+    Chars1 = Chars2,
+    close(Out1),
+    close(Out2)
+)).
+
+% Test 4: Positive timeout should timeout on slow output
+test("positive timeout stops reading", (
+    atom_chars('/usr/bin/python3', Py),
+    atom_chars('-c', C),
+    atom_chars('import sys,time; [print(c,end="",flush=True) or time.sleep(1) for c in "ABCDEFGH"]', Cmd),
+    process_create(Py, [C, Cmd], [stdout(pipe(Out))]),
+
+    get_n_chars(Out, N, _Chars, 2500),
+
+    N >= 2,
+    N =< 3,
+    close(Out)
+)).
+
+% Test 5: infinity atom means no timeout
+test("infinity atom means no timeout", (
+    atom_chars('/bin/echo', Echo),
+    atom_chars('InfinityTest', Content),
+    process_create(Echo, [Content], [stdout(pipe(Out))]),
+
+    get_n_chars(Out, N, _Chars, infinity),
+
+    N > 0,
+    close(Out)
+)).
+
+% Test 6: Stream remains usable after timeout
+test("stream usable after timeout", (
+    atom_chars('/usr/bin/python3', Py),
+    atom_chars('-c', C),
+    atom_chars('import sys,time; print("A",end="",flush=True); time.sleep(2); print("B",end="",flush=True)', Cmd),
+    process_create(Py, [C, Cmd], [stdout(pipe(Out))]),
+
+    get_n_chars(Out, N1, Chars1, 100),
+    get_n_chars(Out, N2, Chars2, 3000),
+
+    N1 = 1,
+    Chars1 = "A",
+    N2 = 1,
+    Chars2 = "B",
+    close(Out)
+)).
+
+% Test 7: Timeout returns partial data, not EOF
+test("timeout returns partial data not EOF", (
+    atom_chars('/usr/bin/python3', Py),
+    atom_chars('-c', C),
+    atom_chars('import sys,time; print("ABC",end="",flush=True); time.sleep(5); print("DEF",end="",flush=True)', Cmd),
+    process_create(Py, [C, Cmd], [stdout(pipe(Out))]),
+
+    get_n_chars(Out, N1, Chars1, 1000),
+    get_n_chars(Out, N2, Chars2, 6000),
+
+    N1 = 3,
+    Chars1 = "ABC",
+    N2 = 3,
+    Chars2 = "DEF",
+    close(Out)
+)).
+
+% Test 8: Multiple reads with timeout=0
+test("multiple reads with timeout=0", (
+    atom_chars('/bin/echo', Echo),
+    atom_chars('ABCDEFGHIJKLMNOP', Content),
+    process_create(Echo, [Content], [stdout(pipe(Out))]),
+
+    get_n_chars(Out, 4, Chars1, 0),
+    get_n_chars(Out, 4, Chars2, 0),
+    get_n_chars(Out, 4, Chars3, 0),
+
+    Chars1 = "ABCD",
+    Chars2 = "EFGH",
+    Chars3 = "IJKL",
+    close(Out)
+)).
+
+% Test 9: Reading more than available with timeout=0
+test("read more than available with timeout=0", (
+    atom_chars('/bin/echo', Echo),
+    atom_chars('Short', Content),
+    process_create(Echo, [Content], [stdout(pipe(Out))]),
+
+    get_n_chars(Out, N, _Chars, 0),
+
+    N >= 5,
+    N =< 7,
+    close(Out)
+)).
+
+% Test 10: Variable N unifies with actual character count
+test("variable N unifies with actual count", (
+    atom_chars('/usr/bin/python3', Py),
+    atom_chars('-c', C),
+    atom_chars('import sys,time; [print(c,end="",flush=True) or time.sleep(0.5) for c in "ABCD"]', Cmd),
+    process_create(Py, [C, Cmd], [stdout(pipe(Out))]),
+
+    get_n_chars(Out, N, Chars, 1300),
+    length(Chars, ActualLength),
+
+    N = ActualLength,
+    close(Out)
+)).

tests/scryer/cli/src_tests/get_n_chars.toml

@@ -0,0 +1 @@
+args = ["-f", "--no-add-history", "src/tests/get_n_chars.pl", "-f", "-g", "use_module(library(get_n_chars_tests)), get_n_chars_tests:main_quiet(get_n_chars_tests)"]