std.debug.assert: remove special case for test builds

Previously, std.debug.assert would `@panic` in test builds,
if the assertion failed. Now, it's always `unreachable`.

This makes release mode test builds more accurately test
the actual code that will be run.

However this requires tests to call `std.testing.expect`
rather than `std.debug.assert` to make sure output is correct.

Here is the explanation of when to use either one, copied from
the assert doc comments:

Inside a test block, it is best to use the `std.testing` module
rather than assert, because assert may not detect a test failure
in ReleaseFast and ReleaseSafe mode. Outside of a test block, assert
is the correct function to use.

closes #1304

1 files changed, 2 insertions, 1 deletions

diff --git a/std/dynamic_library.zig b/std/dynamic_library.zig
index 4d19951318..66026b1f29 100644
--- a/std/dynamic_library.zig
+++ b/std/dynamic_library.zig
@@ -6,6 +6,7 @@ const mem = std.mem;
 const cstr = std.cstr;
 const os = std.os;
 const assert = std.debug.assert;
+const testing = std.testing;
 const elf = std.elf;
 const linux = os.linux;
 const windows = os.windows;
@@ -206,7 +207,7 @@ test "dynamic_library" {
     };
 
     const dynlib = DynLib.open(std.debug.global_allocator, libname) catch |err| {
-        assert(err == error.FileNotFound);
+        testing.expect(err == error.FileNotFound);
         return;
     };
     @panic("Expected error from function");