p_fallocate: add a test for our implementation

tests/core/posix.c

@@ -27,6 +27,11 @@ void test_core_posix__initialize(void)
 #endif
 }
 
+void test_core_posix__cleanup(void)
+{
+    p_unlink("fallocate_test");
+}
+
 static bool supports_ipv6(void)
 {
 #ifdef GIT_WIN32
@@ -190,3 +195,39 @@ void test_core_posix__p_regcomp_compile_userdiff_regexps(void)
 		cl_must_pass(error);
 	}
 }
+
+void test_core_posix__fallocate(void)
+{
+	int fd;
+	struct stat st;
+
+	/* fallocate a new file succeeds */
+	cl_must_pass(fd = p_open("fallocate_test", O_RDWR|O_CREAT, 0666));
+	cl_must_pass(p_fallocate(fd, 0, 42));
+	cl_must_pass(p_fstat(fd, &st));
+	cl_assert_equal_i(42, st.st_size);
+	p_close(fd);
+
+	/* fallocate an existing file succeeds */
+	cl_must_pass(fd = p_open("fallocate_test", O_RDWR, 0666));
+	cl_must_pass(p_fallocate(fd, 90, 9));
+	cl_must_pass(p_fstat(fd, &st));
+	cl_assert_equal_i(99, st.st_size);
+	p_close(fd);
+
+	/* fallocate doesn't shrink */
+	cl_must_pass(fd = p_open("fallocate_test", O_RDWR, 0666));
+	cl_must_pass(p_fallocate(fd, 0, 14));
+	cl_must_pass(p_fstat(fd, &st));
+	cl_assert_equal_i(99, st.st_size);
+	p_close(fd);
+
+	/* fallocate doesn't move the cursor */
+	cl_must_pass(fd = p_open("fallocate_test", O_RDWR, 0666));
+	cl_must_pass(p_fallocate(fd, 0, 100));
+	cl_assert_equal_i(0, p_lseek(fd, 0, SEEK_CUR));
+	cl_must_pass(p_lseek(fd, 42, SEEK_SET));
+	cl_must_pass(p_fallocate(fd, 0, 200));
+	cl_assert_equal_i(42, p_lseek(fd, 0, SEEK_CUR));
+	p_close(fd);
+}