Implement buffer interface and tests

- Implement buffer_open_file/string, buffer_read, buffer_close in v0/src/buffer.c

- Add tests in v0/tests/test_buffer.c and test_buffer.txt; register tests in v0/tests/test.c

- Update v0/include.mk and Makefile

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

v0/tests/test.c

@@ -1,24 +1,65 @@
 #include "test.h"
+#include "../src/buffer.h"
+#include <setjmp.h>
+#include <stdio.h>
 
-// @copilot implement fail()
+static jmp_buf s_testJmp;
+static const char* s_failMsg;
+
+void fail(const char* msg) {
+    s_failMsg = msg;
+    longjmp(s_testJmp, 1);
+}
+
+typedef struct {
+    const char* name;
+    Test func;
+} TestCase;
+
+#include "test_buffer.c"
 
 static int s_totalTests;
 static int s_greenTests;
 
-static Test[] = {
-	// @copilot add all tests
+static TestCase s_tests[] = {
+    {"buffer_string_reads_chars", test_buffer_string_reads_chars},
+    {"buffer_string_eof", test_buffer_string_eof},
+    {"buffer_string_eof_after_content", test_buffer_string_eof_after_content},
+    {"buffer_file_reads_chars", test_buffer_file_reads_chars},
+    {"buffer_file_open_fail", test_buffer_file_open_fail},
 };
 
 int main(int argc, char** argv) {
-	/*
-	@copilot loop over each test.
-	If the test is good, count the test as part of green test.
-	Otherwise, go to the next one.
+    (void)argc;
+    (void)argv;
 
-	The start of the test must log the name of the test method.
-	After the test, log either "[OK]" or "[FAIL]".
+    s_totalTests = sizeof(s_tests) / sizeof(s_tests[0]);
+    s_greenTests = 0;
 
-	At the very end, log the name of each failed test and the total
-	number of green tests compared to the total.
-	*/
+    const char* failedTests[s_totalTests + 1];
+    int failedCount = 0;
+
+    for (int i = 0; i < s_totalTests; i++) {
+        printf("%s...", s_tests[i].name);
+        s_failMsg = NULL;
+
+        if (setjmp(s_testJmp) == 0) {
+            s_tests[i].func();
+            printf(" [OK]\n");
+            s_greenTests++;
+        } else {
+            printf(" [FAIL]: %s\n", s_failMsg ? s_failMsg : "");
+            failedTests[failedCount++] = s_tests[i].name;
+        }
+    }
+
+    if (failedCount > 0) {
+        printf("\nFailed tests:\n");
+        for (int i = 0; i < failedCount; i++) {
+            printf("  - %s\n", failedTests[i]);
+        }
+    }
+
+    printf("\n%d/%d tests passed.\n", s_greenTests, s_totalTests);
+    return failedCount > 0 ? 1 : 0;
 }

v0/tests/test.h

@@ -4,8 +4,7 @@
 #ifndef TEST_H
 #define TEST_H
 
-// @copilot fix the syntax. This is a typedef for any function taking a void and returning void.
-typedef Test void(void);
+typedef void (*Test)(void);
 
 /**
  * Fails a test.

v0/tests/test_buffer.c

@@ -0,0 +1,43 @@
+#include "test.h"
+#include "../src/buffer.h"
+#include <stdio.h>
+
+// @copilot add test for reading from a file.
+// Create test_buffer_xyz.txt if you need multiple,
+// otherwise simply test_buffer.txt
+
+static void test_buffer_string_reads_chars(void) {
+    Buffer* buf = buffer_open_string("hi");
+    if (buffer_read(buf) != 'h') fail("expected 'h'");
+    if (buffer_read(buf) != 'i') fail("expected 'i'");
+    buffer_close(buf);
+}
+
+static void test_buffer_string_eof(void) {
+    Buffer* buf = buffer_open_string("");
+    if (buffer_read(buf) != (char)-1) fail("expected -1 on empty string");
+    buffer_close(buf);
+}
+
+static void test_buffer_string_eof_after_content(void) {
+    Buffer* buf = buffer_open_string("a");
+    buffer_read(buf);
+    if (buffer_read(buf) != (char)-1) fail("expected -1 after end of string");
+    buffer_close(buf);
+}
+
+static void test_buffer_file_reads_chars(void) {
+    Buffer* buf = buffer_open_file("v0/tests/test_buffer.txt");
+    if (buf == NULL) fail("could not open file");
+    if (buffer_read(buf) != 'a') fail("expected 'a'");
+    if (buffer_read(buf) != 'b') fail("expected 'b'");
+    if (buffer_read(buf) != 'c') fail("expected 'c'");
+    if (buffer_read(buf) != '\n') fail("expected newline after content");
+    if (buffer_read(buf) != (char)-1) fail("expected -1 after file");
+    buffer_close(buf);
+}
+
+static void test_buffer_file_open_fail(void) {
+    Buffer* buf = buffer_open_file("v0/tests/does_not_exist.txt");
+    if (buf != NULL) fail("expected NULL for non-existent file");
+}

v0/tests/test_buffer.txt

@@ -0,0 +1 @@
+abc