config: remove test cases for impossible scenarios

AEInterval is overridden by NonUserSource, so there is no way for a user
to set this value. These two cases represented impossible real world
scenarios.

Instead the test is replaced with one that shows that the AEInterval can
not be set by config.

This change allows us to remove the hcltail and jsontail fields from
testCase

agent/config/runtime_test.go

@@ -39,16 +39,14 @@ type testCase struct {
 	desc  string
 	args  []string
 	pre   func()                  // setup(t *testing.T)
-	json  []string
-	hcl   []string
 	patch func(rt *RuntimeConfig) // expected
 	err   string                  // expectedErr
 	warns []string                // expectedWarnings
 
 	opts LoadOpts
 
-	// TODO: move all of these to opts
+	json []string
-	hcltail, jsontail []string
+	hcl  []string
 }
 
 // TestConfigFlagsAndEdgecases tests the command line flags and
@@ -1720,18 +1718,14 @@ func TestLoad_IntegrationWithFlags(t *testing.T) {
 			err: "Multiple public IPv6 addresses found. Please configure one",
 		},
 		{
-			desc:     "ae_interval invalid == 0",
+			desc: "ae_interval is overridden by NonUserSource",
 			args: []string{`-data-dir=` + dataDir},
-			jsontail: []string{`{ "ae_interval": "0s" }`},
+			json: []string{`{ "ae_interval": "-1s" }`},
-			hcltail:  []string{`ae_interval = "0s"`},
+			hcl:  []string{`ae_interval = "-1s"`},
-			err:      `ae_interval cannot be 0s. Must be positive`,
+			patch: func(rt *RuntimeConfig) {
+				rt.DataDir = dataDir
+				rt.AEInterval = time.Minute
 			},
-		{
-			desc:     "ae_interval invalid < 0",
-			args:     []string{`-data-dir=` + dataDir},
-			jsontail: []string{`{ "ae_interval": "-1s" }`},
-			hcltail:  []string{`ae_interval = "-1s"`},
-			err:      `ae_interval cannot be -1s. Must be positive`,
 		},
 		{
 			desc: "acl_datacenter invalid",
@@ -4876,9 +4870,10 @@ func testConfig(t *testing.T, tests []testCase, dataDir string) {
 				t.Fatal(tt.desc, ": JSON and HCL test case out of sync")
 			}
 
-			srcs, tails := tt.json, tt.jsontail
+			// select the source
+			srcs := tt.json
 			if format == "hcl" {
-				srcs, tails = tt.hcl, tt.hcltail
+				srcs = tt.hcl
 			}
 
 			// build the description
@@ -4914,13 +4909,6 @@ func testConfig(t *testing.T, tests []testCase, dataDir string) {
 						Data:   data,
 					})
 				}
-				for i, data := range tails {
-					b.Tail = append(b.Tail, FileSource{
-						Name:   fmt.Sprintf("tail-%d.%s", i, format),
-						Format: format,
-						Data:   data,
-					})
-				}
 
 				actual, err := b.BuildAndValidate()
 				switch {