Added tests.

tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags02.ts

@@ -0,0 +1,42 @@
+// @declaration: true
+
+type Kind = "A" | "B"
+
+interface Entity {
+    kind: Kind;
+}
+
+interface A extends Entity {
+    kind: "A";
+    a: number;
+}
+
+interface B extends Entity {
+    kind: "B";
+    b: string;
+}
+
+function hasKind(entity: Entity, kind: "A"): entity is A;
+function hasKind(entity: Entity, kind: "B"): entity is B;
+function hasKind(entity: Entity, kind: Kind): entity is (A | B) {
+    return entity.kind === kind;
+}
+
+let x: A = {
+    kind: "A",
+    a: 100,
+}
+
+if (hasKind(x, "A")) {
+    let a = x;
+}
+else {
+    let b = x;
+}
+
+if (!hasKind(x, "B")) {
+    let c = x;
+}
+else {
+    let d = x;
+}

tests/cases/conformance/types/stringLiteral/stringLiteralTypesAsTags03.ts

@@ -0,0 +1,46 @@
+// @declaration: true
+
+type Kind = "A" | "B"
+
+interface Entity {
+    kind: Kind;
+}
+
+interface A extends Entity {
+    kind: "A";
+    a: number;
+}
+
+interface B extends Entity {
+    kind: "B";
+    b: string;
+}
+
+// Currently (2015-12-14), we write '"A" | "A"' and '"B" | "B"' to avoid
+// interpreting respective overloads as "specialized" signatures.
+// That way, we can avoid the need to look for a compatible overload
+// signature and simply check compatibility with the implementation.
+function hasKind(entity: Entity, kind: "A" | "A"): entity is A;
+function hasKind(entity: Entity, kind: "B" | "B"): entity is B;
+function hasKind(entity: Entity, kind: Kind): entity is Entity {
+    return entity.kind === kind;
+}
+
+let x: A = {
+    kind: "A",
+    a: 100,
+}
+
+if (hasKind(x, "A")) {
+    let a = x;
+}
+else {
+    let b = x;
+}
+
+if (!hasKind(x, "B")) {
+    let c = x;
+}
+else {
+    let d = x;
+}