add test files

tests/exercises/echo-function/solution/top-level-output.ts

@@ -0,0 +1,13 @@
+function echo(content: Object) {
+    return content;
+}
+
+function noEcho(content: Object) {
+    // Do nothing.
+}
+
+function toString(number: Object): string {
+    return number.toString();
+}
+
+console.log("This is top-level output");

tests/exercises/echo-function/solution/unknown-return-type.ts

@@ -0,0 +1,15 @@
+class Coord {
+
+    public x: number;
+    public y: number;
+
+    constructor(x: number, y: number ) {
+        this.x = x;
+        this.y = y;
+    }
+
+}
+
+function echo(content: unknown) {
+    return new Coord(5, 7);
+}