testharness: allow describe blocks to be skiped with require(...)

When a require(...) call is present in a describe(...) body, it must
produce a successful result in order for the testers within that body
to be evaluated.

testharness/tester.go

@@ -1,6 +1,7 @@
 package testharness
 
 import (
+	"github.com/hashicorp/hcl2/hcl"
 	"github.com/hashicorp/terraform/tfdiags"
 	lua "github.com/yuin/gopher-lua"
 )
@@ -83,6 +84,7 @@ func (t *describe) test(subject *Subject, cs CheckStream) {
 		return
 	}
 
+Contexts:
 	for _, childContext := range childContexts {
 		L := childContext.lstate
 		var diags tfdiags.Diagnostics
@@ -126,15 +128,38 @@ func (t *describe) test(subject *Subject, cs CheckStream) {
 			continue
 		}
 
-		if testersB.Skip {
-			// testersB.Skip is set if there's a call to require() in
-			// the body and the given condition didn't hold.
-			cs.Write(CheckItem{
-				Result:  Skipped,
-				Caption: childContext.Name(),
-				Diags:   diags,
-			})
-			continue
+		for _, requirement := range testersB.Requirements {
+			switch requirement.Result() {
+			case Skipped:
+				diags = diags.Append(&hcl.Diagnostic{
+					Severity: hcl.DiagError,
+					Summary:  "Requirement created without assertion",
+					Detail:   "An assertion method must be called on the result of each \"require\" call.",
+					Subject:  requirement.defRange.ToHCL().Ptr(),
+				})
+				cs.Write(CheckItem{
+					Result:  Error,
+					Caption: childContext.Name(),
+					Diags:   diags,
+				})
+				continue Contexts
+			case Error:
+				diags = diags.Append(requirement.diags)
+				cs.Write(CheckItem{
+					Result:  Error,
+					Caption: childContext.Name(),
+					Diags:   diags,
+				})
+				continue Contexts
+			case Failure:
+				// TODO: Do something with the detail message from the requirement, if any.
+				cs.Write(CheckItem{
+					Result:  Skipped,
+					Caption: childContext.Name(),
+					Diags:   diags,
+				})
+				continue Contexts
+			}
 		}
 
 		for _, tester := range testersB.Testers {

testharness/testers_builder.go

@@ -16,13 +16,15 @@ type testersBuilder struct {
 	Context *Context
 	Testers Testers
 	Diags   *Diagnostics
-	Skip    bool
+
+	Requirements []*expect
 }
 
 func (b *testersBuilder) luaTesterDecls(L *lua.LState) map[lua.LString]lua.LValue {
 	return map[lua.LString]lua.LValue{
 		"describe": L.NewFunction(b.luaDescribeFunc),
 		"it":       L.NewFunction(b.luaItFunc),
+		"require":  L.NewFunction(b.luaRequireFunc),
 	}
 }
 
@@ -124,6 +126,38 @@ func (b *testersBuilder) luaItFunc(L *lua.LState) int {
 	return 0
 }
 
+func (b *testersBuilder) luaRequireFunc(L *lua.LState) int {
+	defRangeHCL := callingRange(L, 1)
+	var defRange tfdiags.SourceRange
+	if defRangeHCL != nil {
+		defRange = tfdiags.SourceRangeFromHCL(*defRangeHCL)
+	}
+
+	if L.GetTop() != 1 {
+		b.Diags.Append(&hcl.Diagnostic{
+			Severity: hcl.DiagError,
+			Summary:  "Invalid \"require\" call",
+			Detail:   "A \"require\" call must have one argument: the given value to make an assertion about.",
+			Subject:  defRangeHCL,
+		})
+
+		// We'll still return a requirement object just so the subsequent
+		// method call doesn't _also_ fail here. It'll never actually
+		// be evaluated (since it's not in the requirements list) so doesn't
+		// really matter what value we set it to.
+		stubRequirement := newExpect(b.Context.lstate, lua.LNil, defRange)
+		L.Push(stubRequirement.LuaObject())
+		return 1
+	}
+
+	given := L.CheckAny(1)
+
+	requirement := newExpect(b.Context.lstate, given, defRange)
+	b.Requirements = append(b.Requirements, requirement)
+	L.Push(requirement.LuaObject())
+	return 1
+}
+
 func (b *testersBuilder) luaContextSetters(L *lua.LState) map[lua.LString]lua.LValue {
 	return map[lua.LString]lua.LValue{
 		"resource": b.luaResourceObj(L),