test: set case name from initial filename for a sequence

Port more incremental tests.

test/incremental/assert_function.13.zig

@@ -0,0 +1,19 @@
+pub fn main() void {
+    const ignore =
+        \\ cool thx
+        \\
+    ;
+    _ = ignore;
+    add('ぁ', '\x03');
+}
+
+fn add(a: u32, b: u32) void {
+    assert(a + b == 12356);
+}
+
+pub fn assert(ok: bool) void {
+    if (!ok) unreachable; // assertion failure
+}
+
+// run
+//