lib/strings+test: port join from Hare str... variadic (#19)

lib/strings/stringstest.ww

@@ -99,6 +99,62 @@ fn streq(a: str, b: str) bool = {
 	};
 };
 
+// ---- join -------------------------------------------------------------
+// ref/hare/strings/concat.ha:64. Rows mirror Hare's @test fn join
+// (0-arg, 1-arg, empty-sep, 3-arg.) plus 2-arg, all-empties, long sep,
+// multibyte, empty-mid (delim still inserted around the empty slot).
+// Per-row `signalled` 1620+i narrows the failing row.
+
+@test fn join_cases() void = {
+	let pool: [19]str;
+	pool[0]  = "hello";
+	pool[1]  = "a";
+	pool[2]  = "b";
+	pool[3]  = "a";
+	pool[4]  = "b";
+	pool[5]  = "c";
+	pool[6]  = "a";
+	pool[7]  = "b";
+	pool[8]  = "c";
+	pool[9]  = "";
+	pool[10] = "";
+	pool[11] = "a";
+	pool[12] = "b";
+	pool[13] = "c";
+	pool[14] = "こん";
+	pool[15] = "にちは";
+	pool[16] = "a";
+	pool[17] = "";
+	pool[18] = "b";
+
+	let argo:   [9]i32;
+	let argn:   [9]i32;
+	let seps:   [9]str;
+	let want:   [9]str;
+	argo[0]=0;  argn[0]=0; seps[0]=".";    want[0]="";
+	argo[1]=0;  argn[1]=1; seps[1]=".";    want[1]="hello";
+	argo[2]=1;  argn[2]=2; seps[2]=", ";   want[2]="a, b";
+	argo[3]=3;  argn[3]=3; seps[3]=".";    want[3]="a.b.c";
+	argo[4]=6;  argn[4]=3; seps[4]="";     want[4]="abc";
+	argo[5]=9;  argn[5]=2; seps[5]=",";    want[5]=",";
+	argo[6]=11; argn[6]=3; seps[6]=" :: "; want[6]="a :: b :: c";
+	argo[7]=14; argn[7]=2; seps[7]="・";   want[7]="こん・にちは";
+	argo[8]=16; argn[8]=3; seps[8]="-";    want[8]="a--b";
+
+	let i: i32 = 0;
+	for (i < 9) {
+		signalled = 1620 + i;
+		let argv: []str;
+		argv.ptr = &pool[argo[i]];
+		argv.len = argn[i];
+		argv.cap = argn[i];
+		let got: str = strings.join(seps[i], argv...);
+		if (!streq(got, want[i])) { fail(); };
+		if (got.len > 0) { os.free(got.ptr: *void, got.len: u64); };
+		i += 1;
+	};
+};
+
 // ---- hasprefix --------------------------------------------------------
 // ref/hare/strings/suffix.ha:18.
 
@@ -842,6 +898,7 @@ fn streq(a: str, b: str) bool = {
 export fn main() i32 = {
 	signalled = 1;  dup_cases();
 	signalled = 2;  concat_cases();
+	signalled = 30; join_cases();
 	signalled = 3;  hasprefix_cases();
 	signalled = 4;  hassuffix_cases();
 	signalled = 5;  contains_cases();