test: set case name from initial filename for a sequence

Port more incremental tests.

test/incremental/assert_function.18.zig

@@ -0,0 +1,35 @@
+const builtin = @import("builtin");
+
+extern "c" fn write(usize, usize, usize) usize;
+
+pub fn main() void {
+    for ("hello") |_| print();
+}
+
+fn print() void {
+    switch (builtin.os.tag) {
+        .linux => {
+            asm volatile ("syscall"
+                :
+                : [number] "{rax}" (1),
+                  [arg1] "{rdi}" (1),
+                  [arg2] "{rsi}" (@ptrToInt("hello\n")),
+                  [arg3] "{rdx}" (6),
+                : "rcx", "r11", "memory"
+            );
+        },
+        .macos => {
+            _ = write(1, @ptrToInt("hello\n"), 6);
+        },
+        else => unreachable,
+    }
+}
+
+// run
+//
+// hello
+// hello
+// hello
+// hello
+// hello
+//